item assignment in string python

TypeError: 'str' object does not support item assignment

Last updated: Apr 8, 2024 Reading time · 8 min

# Table of Contents

TypeError: 'int' object does not support item assignment
'numpy.float64' object does not support item assignment

# TypeError: 'str' object does not support item assignment

The Python "TypeError: 'str' object does not support item assignment" occurs when we try to modify a character in a string.

Strings are immutable in Python, so we have to convert the string to a list, replace the list item and join the list elements into a string.

Here is an example of how the error occurs.

We tried to change a specific character of a string which caused the error.

Strings are immutable, so updating the string in place is not an option.

Instead, we have to create a new, updated string.

# Using str.replace() to get a new, updated string

One way to solve the error is to use the str.replace() method to get a new, updated string.

using str replace to get new updated string

The str.replace() method returns a copy of the string with all occurrences of a substring replaced by the provided replacement.

The method takes the following parameters:

Name	Description
old	The substring we want to replace in the string
new	The replacement for each occurrence of
count	Only the first occurrences are replaced (optional)

By default, the str.replace() method replaces all occurrences of the substring in the string.

If you only need to replace the first occurrence, set the count argument to 1 .

Setting the count argument to 1 means that only the first occurrence of the substring is replaced.

# Replacing a character with a conversion to list

One way to replace a character at a specific index in a string is to:

Convert the string to a list.
Update the list item at the specified index.
Join the list items into a string.

replace character with conversion to list

We passed the string to the list() class to get a list containing the string's characters.

The last step is to join the list items into a string with an empty string separator.

The str.join() method takes an iterable as an argument and returns a string which is the concatenation of the strings in the iterable.

Python indexes are zero-based, so the first character in a string has an index of 0 , and the last character has an index of -1 or len(a_string) - 1 .

If you have to do this often, define a reusable function.

The update_str function takes a string, index and new characters as parameters and returns a new string with the character at the specified index updated.

An alternative approach is to use string slicing .

# Reassigning a string variable

If you need to reassign a string variable by adding characters to it, use the += operator.

The += operator is a shorthand for my_str = my_str + 'new' .

The code sample achieves the same result as using the longer form syntax.

# Using string slicing to get a new, updated string

Here is an example that replaces an underscore at a specific index with a space.

using string slicing to get new updated string

The first piece of the string we need is up to, but not including the character we want to replace.

The syntax for string slicing is a_string[start:stop:step] .

The start index is inclusive, whereas the stop index is exclusive (up to, but not including).

The slice my_str[0:idx] starts at index 0 and goes up to, but not including idx .

The next step is to use the addition + operator to add the replacement string (in our case - a space).

The last step is to concatenate the rest of the string.

Notice that we start the slice at index + 1 because we want to omit the character we are replacing.

We don't specify an end index after the colon, therefore the slice goes to the end of the string.

We simply construct a new string excluding the character at the specified index and providing a replacement string.

If you have to do this often define a reusable function.

The function takes a string, index and a replacement character as parameters and returns a new string with the character at the specified index replaced.

If you need to update multiple characters in the function, use the length of the replacement string when slicing.

The function takes one or more characters and uses the length of the replacement string to determine the start index for the second slice.

If the user passes a replacement string that contains 2 characters, then we omit 2 characters from the original string.

# TypeError: 'int' object does not support item assignment

The Python "TypeError: 'int' object does not support item assignment" occurs when we try to assign a value to an integer using square brackets.

To solve the error, correct the assignment or the accessor, as we can't mutate an integer value.

We tried to change the digit at index 0 of an integer which caused the error.

# Declaring a separate variable with a different name

If you meant to declare another integer, declare a separate variable with a different name.

# Changing an integer value in a list

Primitives like integers, floats and strings are immutable in Python.

If you meant to change an integer value in a list, use square brackets.

Python indexes are zero-based, so the first item in a list has an index of 0 , and the last item has an index of -1 or len(a_list) - 1 .

We used square brackets to change the value of the list element at index 0 .

# Updating a value in a two-dimensional list

If you have two-dimensional lists, you have to access the list item at the correct index when updating it.

We accessed the first nested list (index 0 ) and then updated the value of the first item in the nested list.

# Reassigning a list to an integer by mistake

Make sure you haven't declared a variable with the same name multiple times and you aren't reassigning a list to an integer somewhere by mistake.

We initially declared the variable and set it to a list, however, it later got set to an integer.

Trying to assign a value to an integer causes the error.

To solve the error, track down where the variable got assigned an integer and correct the assignment.

# Getting a new list by running a computation

If you need to get a new list by running a computation on each integer value of the original list, use a list comprehension .

The Python "TypeError: 'int' object does not support item assignment" is caused when we try to mutate the value of an int.

# Checking what type a variable stores

If you aren't sure what type a variable stores, use the built-in type() class.

The type class returns the type of an object.

The isinstance() function returns True if the passed-in object is an instance or a subclass of the passed-in class.

# 'numpy.float64' object does not support item assignment

The Python "TypeError: 'numpy.float64' object does not support item assignment" occurs when we try to assign a value to a NumPy float using square brackets.

To solve the error, correct the assignment or the accessor, as we can't mutate a floating-point number.

We tried to change the digit at index 0 of a NumPy float.

# Declaring multiple floating-point numbers

If you mean to declare another floating-point number, simply declare a separate variable with a different name.

# Floating-point numbers are immutable

Primitives such as floats, integers and strings are immutable in Python.

If you need to update a value in an array of floating-point numbers, use square brackets.

We changed the value of the array element at index 0 .

# Reassigning a variable to a NumPy float by mistake

Make sure you haven't declared a variable with the same name multiple times and you aren't reassigning a list to a float somewhere by mistake.

We initially set the variable to a NumPy array but later reassigned it to a floating-point number.

Trying to update a digit in a float causes the error.

# When working with two-dimensional arrays

If you have a two-dimensional array, access the array element at the correct index when updating it.

We accessed the first nested array (index 0 ) and then updated the value of the first item in the nested array.

The Python "TypeError: 'float' object does not support item assignment" is caused when we try to mutate the value of a float.

Borislav Hadzhiev

Web Developer

[Solved] TypeError: ‘str’ Object Does Not Support Item Assignment

In this article, we will be discussing the TypeError:’str’ Object Does Not Support Item Assignment exception . We will also be going through solutions to this problem with example programs.

Why is This Error Raised?

When you attempt to change a character within a string using the assignment operator, you will receive the Python error TypeError: ‘str’ object does not support item assignment.

As we know, strings are immutable. If you attempt to change the content of a string, you will receive the error TypeError: ‘str’ object does not support item assignment .

There are four other similar variations based on immutable data types :

TypeError: 'tuple' object does not support item assignment
TypeError: 'int' object does not support item assignment
TypeError: 'float' object does not support item assignment
TypeError: 'bool' object does not support item assignment

Replacing String Characters using Assignment Operators

Replicate these errors yourself online to get a better idea here .

In this code, we will attempt to replace characters in a string.

Strings are an immutable data type. However, we can change the memory to a different set of characters like so:

TypeError: ‘str’ Object Does Not Support Item Assignment in JSON

Let’s review the following code, which retrieves data from a JSON file.

In line 5, we are assigning data['sample'] to a string instead of an actual dictionary. This causes the interpreter to believe we are reassigning the value for an immutable string type.

TypeError: ‘str’ Object Does Not Support Item Assignment in PySpark

The following program reads files from a folder in a loop and creates data frames.

This occurs when a PySpark function is overwritten with a string. You can try directly importing the functions like so:

TypeError: ‘str’ Object Does Not Support Item Assignment in PyMongo

The following program writes decoded messages in a MongoDB collection. The decoded message is in a Python Dictionary.

At the 10th visible line, the variable x is converted as a string.

It’s better to use:

Please note that msg are a dictionary and NOT an object of context.

TypeError: ‘str’ Object Does Not Support Item Assignment in Random Shuffle

The below implementation takes an input main and the value is shuffled. The shuffled value is placed into Second .

random.shuffle is being called on a string, which is not supported. Convert the string type into a list and back to a string as an output in Second

TypeError: ‘str’ Object Does Not Support Item Assignment in Pandas Data Frame

The following program attempts to add a new column into the data frame

The iteration statement for dataset in df: loops through all the column names of “sample.csv”. To add an extra column, remove the iteration and simply pass dataset['Column'] = 1 .

[Solved] runtimeerror: cuda error: invalid device ordinal

These are the causes for TypeErrors : – Incompatible operations between 2 operands: – Passing a non-callable identifier – Incorrect list index type – Iterating a non-iterable identifier.

The data types that support item assignment are: – Lists – Dictionaries – and Sets These data types are mutable and support item assignment

As we know, TypeErrors occur due to unsupported operations between operands. To avoid facing such errors, we must: – Learn Proper Python syntax for all Data Types. – Establish the mutable and immutable Data Types. – Figure how list indexing works and other data types that support indexing. – Explore how function calls work in Python and various ways to call a function. – Establish the difference between an iterable and non-iterable identifier. – Learn the properties of Python Data Types.

We have looked at various error cases in TypeError:’str’ Object Does Not Support Item Assignment. Solutions for these cases have been provided. We have also mentioned similar variations of this exception.

Python ‘str’ object does not support item assignment solution

Strings in Python are immutable. This means that they cannot be changed. If you try to change the contents of an existing string, you’re liable to find an error that says something like “‘str’ object does not support item assignment”.

In this guide, we’re going to talk about this common Python error and how it works. We’ll walk through a code snippet with this error present so we can explore how to fix it.

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The problem: ‘str’ object does not support item assignment.

Let’s start by taking a look at our error: Typeerror: ‘str’ object does not support item assignment.

This error message tells us that a string object (a sequence of characters) cannot be assigned an item. This error is raised when you try to change the value of a string using the assignment operator.

The most common scenario in which this error is raised is when you try to change a string by its index values . The following code yields the item assignment error:

You cannot change the character at the index position 0 because strings are immutable.

You should check to see if there are any string methods that you can use to create a modified copy of a string if applicable. You could also use slicing if you want to create a new string based on parts of an old string.

An Example Scenario

We’re going to write a program that checks whether a number is in a string. If a number is in a string, it should be replaced with an empty string. This will remove the number. Our program is below:

This code accepts a username from the user using the input() method . It then loops through every character in the username using a for loop and checks if that character is a number. If it is, we try to replace that character with an empty string. Let’s run our code and see what happens:

Our code has returned an error.

The cause of this error is that we’re trying to assign a string to an index value in “name”:

The Solution

We can solve this error by adding non-numeric characters to a new string. Let’s see how it works:

This code replaces the character at name[c] with an empty string.

We have created a separate variable called “final_username”. This variable is initially an empty string. If our for loop finds a character that is not a number, that character is added to the end of the “final_username” string. Otherwise, nothing happens. We check to see if a character is a number using the isnumeric() method.

We add a character to the “final_username” string using the addition assignment operator. This operator adds one value to another value. In this case, the operator adds a character to the end of the “final_username” string.

Let’s run our code:

Our code successfully removed all of the numbers from our string. This code works because we are no longer trying to change an existing string. We instead create a new string called “final_username” to which we add all the letter-based characters from our username string.

In Python, strings cannot be modified. You need to create a new string based on the contents of an old one if you want to change a string.

The “‘str’ object does not support item assignment” error tells you that you are trying to modify the value of an existing string.

Now you’re ready to solve this Python error like an expert.

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Fix Python TypeError: 'str' object does not support item assignment

This error occurs because a string in Python is immutable, meaning you can’t change its value after it has been defined.

Another way you can modify a string is to use the string slicing and concatenation method.

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Python String Error: ‘str’ Object Does Not Support Item Assignment

If you have encountered the error message “Python String Error: ‘str’ Object Does Not Support Item Assignment,” then you may have been attempting to modify a string object directly or assigning an item to a string object incorrectly.

This error message indicates that the ‘str’ object type in Python is immutable, meaning that once a string object is created, it cannot be modified.

In this article, we will dive into the details of this error message, explore why it occurs, and provide solutions and best practices to resolve and prevent it.

By the end of this article, you will have a better understanding of how to work with strings in Python and avoid common mistakes that lead to this error.

Table of Contents

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Understanding the error message

When encountering the Python String Error: ‘str’ Object Does Not Support Item Assignment, it’s essential to understand what the error message means.

This error message typically occurs when one attempts to modify a string directly through an item assignment.

Strings in Python are immutable, meaning that their contents cannot be changed once they have been created. Therefore, when trying to assign an item to a string object, the interpreter throws this error message.

For example, consider the following code snippet:

string = “hello” string[0] = “H”

When executing this code, the interpreter will raise the Python String Error: ‘str’ Object Does Not Support Item Assignment. Since strings are immutable in Python, it’s impossible to change any individual character in the string object through item assignment.

It’s important to note that this error message is solely related to item assignment. Other string manipulations, such as concatenation and slicing, are still possible.

Understanding the ‘str’ object

The ‘str’ object is a built-in data type in Python and stands for string. Strings are a collection of characters enclosed within single or double quotes, and in Python, these strings are immutable.

While it’s impossible to modify an existing string directly, we can always create a new string using string manipulation functions like concatenation, replace, and split, among others.

In fact, these string manipulation functions are specifically designed to work on immutable strings and provide a wide range of flexibility when working with strings.

Common causes of the error

The “Python String Error: ‘str’ Object Does Not Support Item Assignment” error can occur due to various reasons. Here are some of the common causes:

1. Attempting to modify a string directly

Strings are immutable data types, meaning their values cannot be changed after creation.

Therefore, trying to modify a string directly by assigning a new value to a specific index or item will result in the “Python String Error: ‘str’ Object Does Not Support Item Assignment” error.

string = "Hello World" string[0] = "h"

This will result in the following error message:

TypeError: 'str' object does not support item assignment

2. Misunderstanding the immutability of string objects

As mentioned earlier, string objects are immutable, unlike other data types like lists or dictionaries.

Thus, attempting to change the value of a string object after it is created will result in the “Python String Error: ‘str’ Object Does Not Support Item Assignment” error.

string = "Hello World" string += "!" string[0] = "h"

3. Using the wrong data type for assignment

If you are trying to assign a value of the wrong data type to a string, such as a list or tuple, you can encounter the “Python String Error: ‘str’ Object Does Not Support Item Assignment” error.

string = "Hello World" string[0] = ['h']

TypeError: 'list' object does not support item assignment

Ensure that you use the correct data type when assigning values to a string object to avoid this error.

Resolving the error

There are several techniques available to fix the Python string error: ‘str’ Object Does Not Support Item Assignment.

Here are some solutions:

Using string manipulation methods

One way to resolve the error is to use string manipulation functions that do not require item assignment.

For example, to replace a character in a string at a specific index, use the replace() method instead of assigning a new value to the index. Similarly, to delete a character at a particular position, use the slice() method instead of an item assignment.

Creating a new string object

If you need to modify a string, you can create a new string object based on the original.

One way to modify text is by combining the portions before and after the edited section. This can be achieved by concatenating substrings.

Alternatively, you can use string formatting techniques to insert new values into the string.

Converting the string to a mutable data type

Strings are immutable, which means that their contents cannot be changed.

Nevertheless, you can convert a string to a mutable data type such as a list, modify the list, and then convert it back to a string. Be aware that this approach can have performance implications, especially for larger strings.

When implementing any of these solutions, it’s essential to keep in mind the context of your code and consider the readability and maintainability of your solution.

Best practices to avoid the error

To avoid encountering the “Python String Error: ‘str’ Object Does Not Support Item Assignment,” following some best practices when working with string objects is important.

Here are some tips:

1. Understand string immutability

Strings are immutable objects in Python, meaning they cannot be changed once created.

Attempting to modify a string directly will result in an error. Instead, create a new string object or use string manipulation methods.

2. Use appropriate data types

When creating variables, it is important to use the appropriate data type. If you need to modify a string, consider using a mutable data type such as a list or bytearray instead.

3. Utilize string manipulation functions effectively

Python provides many built-in string manipulation functions that can be used to modify strings without encountering this error. Some commonly used functions include:

replace() – replaces occurrences of a substring with a new string
split() – splits a string into a list of substrings
join() – combines a list of strings into a single string
format() – formats a string with variables

4. Avoid using index-based assignment

Index-based assignment (e.g. string[0] = ‘a’) is not supported for strings in Python. Instead, you can create a new string with the modified value.

5. Be aware of context

When encountering this error, it is important to consider the context in which it occurred. Sometimes, it may be due to a simple syntax error or a misunderstanding of how strings work.

Taking the time to understand the issue and troubleshoot the code can help prevent encountering the error in the future.

By following these best practices and familiarizing yourself with string manipulation methods and data types, you can avoid encountering the “Python String Error: ‘str’ Object Does Not Support Item Assignment” and efficiently work with string objects in Python.

FAQ – Frequently asked questions

Here are some commonly asked questions regarding the ‘str’ object item assignment error:

Q: Why am I getting a string error while trying to modify a string?

A: Python string objects are immutable, meaning they cannot be changed once created. Therefore, you cannot modify a string object directly. Instead, you must create a new string object with the desired modifications.

Q: What is an example of an item assignment with a string object?

A: An example of an item assignment with a string object is attempting to change a character in a string by using an index. For instance, if you try to modify the second character in the string ‘hello’ to ‘i’, as in ‘hillo’, you will get the ‘str’ object item assignment error.

Q: How can I modify a string object?

A: There are a few ways to modify a string object, such as using string manipulation functions like replace() or split(), creating a new string with the desired modifications, or converting the string object to a mutable data type like a list and then modifying it.

Q: Can I prevent encountering this error in the future?

A: Yes, here are some best practices to avoid encountering this error: use appropriate data types for the task at hand, understand string immutability, and use string manipulation functions effectively.

Diving deeper into Python data structures and understanding their differences, advantages, and limitations is also helpful.

Q: Why do I need to know about this error?

A: Understanding the ‘str’ object item assignment error is essential for correctly handling and modifying strings in Python.

This error is a common source of confusion and frustration among Python beginners, and resolving it requires a solid understanding of string immutability, data types, and string manipulation functions.

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How to Fix STR Object Does Not Support Item Assignment Error in Python

Python How-To's
How to Fix STR Object Does Not Support …

In Python, strings are immutable, so we will get the str object does not support item assignment error when trying to change the string.

You can not make some changes in the current value of the string. You can either rewrite it completely or convert it into a list first.

This whole guide is all about solving this error. Let’s dive in.

Fix str object does not support item assignment Error in Python

As the strings are immutable, we can not assign a new value to one of its indexes. Take a look at the following code.

The above code will give o as output, and later it will give an error once a new value is assigned to its fourth index.

The string works as a single value; although it has indexes, you can not change their value separately. However, if we convert this string into a list first, we can update its value.

The above code will run perfectly.

First, we create a list of string elements. As in the list, all elements are identified by their indexes and are mutable.

We can assign a new value to any of the indexes of the list. Later, we can use the join function to convert the same list into a string and store its value into another string.

Haider specializes in technical writing. He has a solid background in computer science that allows him to create engaging, original, and compelling technical tutorials. In his free time, he enjoys adding new skills to his repertoire and watching Netflix.

How to Solve Python TypeError: ‘str’ object does not support item assignment

by Suf | Programming , Python , Tips

Strings are immutable objects, which means you cannot change them once created. If you try to change a string in place using the indexing operator [], you will raise the TypeError: ‘str’ object does not support item assignment.

To solve this error, you can use += to add characters to a string.

a += b is the same as a = a + b

Generally, you should check if there are any string methods that can create a modified copy of the string for your needs.

This tutorial will go through how to solve this error and solve it with the help of code examples.

Python typeerror: ‘str’ object does not support item assignment, solution #1: create new string using += operator, solution #2: create new string using str.join() and list comprehension.

Let’s break up the error message to understand what the error means. TypeError occurs whenever you attempt to use an illegal operation for a specific data type.

The part 'str' object tells us that the error concerns an illegal operation for strings.

The part does not support item assignment tells us that item assignment is the illegal operation we are attempting.

Strings are immutable objects which means we cannot change them once created. We have to create a new string object and add the elements we want to that new object. Item assignment changes an object in place, which is only suitable for mutable objects like lists. Item assignment is suitable for lists because they are mutable.

Let’s look at an example of assigning items to a list. We will iterate over a list and check if each item is even. If the number is even, we will assign the square of that number in place at that index position.

Let’s run the code to see the result:

We can successfully do item assignment on a list.

Let’s see what happens when we try to change a string using item assignment:

We cannot change the character at position -1 (last character) because strings are immutable. We need to create a modified copy of a string, for example using replace() :

In the above code, we create a copy of the string using = and call the replace function to replace the lower case h with an upper case H .

Let’s look at another example.

In this example, we will write a program that takes a string input from the user, checks if there are vowels in the string, and removes them if present. First, let’s define the vowel remover function.

We check if each character in a provided string is a member of the vowels list in the above code. If the character is a vowel, we attempt to replace that character with an empty string. Next, we will use the input() method to get the input string from the user.

Altogether, the program looks like this:

The error occurs because of the line: string[ch] = "" . We cannot change a string in place because strings are immutable.

We can solve this error by creating a modified copy of the string using the += operator. We have to change the logic of our if statement to the condition not in vowels . Let’s look at the revised code:

Note that in the vowel_remover function, we define a separate variable called new_string , which is initially empty. If the for loop finds a character that is not a vowel, we add that character to the end of the new_string string using += . We check if the character is not a vowel with the if statement: if string[ch] not in vowels .

We successfully removed all vowels from the string.

We can solve this error by creating a modified copy of the string using list comprehension. List comprehension provides a shorter syntax for creating a new list based on the values of an existing list.

Let’s look at the revised code:

In the above code, the list comprehension creates a new list of characters from the string if the characters are not in the list of vowels. We then use the join() method to convert the list to a string. Let’s run the code to get the result:

We successfully removed all vowels from the input string.

Congratulations on reading to the end of this tutorial. The TypeError: ‘str’ object does not support item assignment occurs when you try to change a string in-place using the indexing operator [] . You cannot modify a string once you create it. To solve this error, you need to create a new string based on the contents of the existing string. The common ways to change a string are:

List comprehension
The String replace() method
+= Operator

For further reading on TypeErrors, go to the articles:

How to Solve Python TypeError: object of type ‘NoneType’ has no len()
How to Solve Python TypeError: ‘>’ not supported between instances of ‘str’ and ‘int’
How to Solve Python TypeError: ‘tuple’ object does not support item assignment
How to Solve Python TypeError: ‘set’ object does not support item assignment

To learn more about Python for data science and machine learning, go to the online courses page on Python for the most comprehensive courses available.

Have fun and happy researching!

Error	Description	Solution
TypeError: str object does not support item assignment	This error occurs when you try to assign a value to an element of a string.	To fix this error, make sure that you are trying to assign a value to a list or dictionary, not a string.

3. What does it mean for an `str` object to not support item assignment?

In Python, an `str` object is a sequence of characters. As such, it can be indexed and sliced, just like a list. However, unlike a list, an `str` object does not support item assignment. This means that you cannot change the value of a particular character in an `str` object by assigning a new value to that character’s index.

For example, the following code will raise a `TypeError`:

python >>> str = “Hello world” >>> str[0] = “J” Traceback (most recent call last): File “ “, line 1, in TypeError: ‘str’ object does not support item assignment

The reason for this is that an `str` object is immutable, which means that its contents cannot be changed once it has been created. This is in contrast to a `list`, which is mutable, and whose contents can be changed at any time.

The immutability of `str` objects is one of the reasons why they are so efficient. Because their contents cannot be changed, they can be stored in memory more compactly than mutable objects. This can make a big difference in performance, especially for large strings.

If you need to change the value of a particular character in an `str` object, you can use the `replace()` method. The `replace()` method takes two arguments: the old character and the new character. For example, the following code will change the first character in the string `”Hello world”` to the letter `”J”`:

python >>> str = “Hello world” >>> str.replace(“H”, “J”) “Jello world”

The `replace()` method is a more efficient way to change the value of a particular character in an `str` object than using item assignment, because it does not require the entire string to be re-created.

4. How to avoid `TypeError`s when working with `str` objects

There are a few things you can do to avoid `TypeError`s when working with `str` objects:

* **Use the `replace()` method to change the value of a particular character in an `str` object.** As mentioned above, the `replace()` method is a more efficient way to change the value of a particular character in an `str` object than using item assignment. * **Use the `slice()` method to access a substring of an `str` object.** The `slice()` method takes two arguments: the start index and the end index. The start index is the position of the first character in the substring, and the end index is the position of the character after the last character in the substring. For example, the following code will return the substring of the string `”Hello world”` from the first character to the fourth character:

python >>> str = “Hello world” >>> str[0:4] “Hello”

* **Use the `str()` function to convert a non-string object to a string.** If you need to use a non-string object as an argument to a function that expects a string, you can use the `str()` function to convert the non-string object to a string. For example, the following code will print the string representation of the number 12345:

python >>> number = 12345 >>> print(str(number)) “12345”

By following these tips, you can avoid `TypeError`s when working with `str` objects.

In this article, we discussed what it means for an `str` object to not support item assignment. We also provided some tips on how to avoid `TypeError`s when working with `str` objects.

If you have any questions or comments, please feel free to leave them below.

Q: What does the Python error “TypeError: str object does not support item assignment” mean? A: This error occurs when you try to assign a value to an item in a string using the square bracket notation. For example, the following code will raise an error:

python >>> str1 = “hello” >>> str1[0] = “j” Traceback (most recent call last): File “ “, line 1, in TypeError: ‘str’ object does not support item assignment

The reason for this error is that strings are immutable, which means that they cannot be changed after they are created. Therefore, you cannot assign a new value to an item in a string.

Q: How can I avoid this error? A: There are a few ways to avoid this error. One way is to use a list instead of a string. For example, the following code will not raise an error:

python >>> str1 = [“h”, “e”, “l”, “l”, “o”] >>> str1[0] = “j” >>> str1 [‘j’, ‘e’, ‘l’, ‘l’, ‘o’]

Another way to avoid this error is to use the `replace()` method. The `replace()` method allows you to replace a character in a string with a new character. For example, the following code will not raise an error:

python >>> str1 = “hello” >>> str1 = str1.replace(“h”, “j”) >>> str1 “jello”

Q: What other errors are related to string objects? A: There are a few other errors that are related to string objects. These errors include:

`ValueError: invalid literal for int() with base 10: ‘a’`: This error occurs when you try to convert a string to an integer, but the string contains a character that is not a digit.
`IndexError: string index out of range`: This error occurs when you try to access an item in a string that does not exist.
`TypeError: can’t concatenate str and int`: This error occurs when you try to concatenate a string with an integer.

Q: How can I learn more about string objects in Python? A: There are a few resources that you can use to learn more about string objects in Python. These resources include:

The [Python documentation on strings](https://docs.python.org/3/library/stdtypes.htmlstring-objects)
The [Python tutorial on strings](https://docs.python.org/3/tutorial/.htmlstrings)
The [Python reference on strings](https://docs.python.org/3/reference/lexical_analysis.htmlstrings)

Q: Is there anything else I should know about string objects in Python? A: There are a few other things that you should know about string objects in Python. These include:

Strings are enclosed in single or double quotes.
Strings can contain any character, including letters, numbers, and special characters.
Strings can be concatenated using the `+` operator.
Strings can be repeated using the `*` operator.
Strings can be indexed using the `[]` operator.
Strings can be sliced using the `[start:end]` operator.
Strings can be converted to other data types using the `str()` function.
Strings can be checked for equality using the `==` operator.
Strings can be checked for inequality using the `!=` operator.

I hope this helps!

In this blog post, we discussed the Python TypeError: str object does not support item assignment error. We explained what this error means and how to fix it. We also provided some tips on how to avoid this error in the future.

Here are the key takeaways from this blog post:

The Python TypeError: str object does not support item assignment error occurs when you try to assign a value to a string using the square bracket notation.
To fix this error, you can either use the string’s replace() method or the slice notation.
To avoid this error in the future, be careful not to use the square bracket notation with strings.

We hope this blog post was helpful! If you have any other questions about Python, please feel free to contact us.

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Python Strings

In Python, a string is a sequence of characters. For example, "hello" is a string containing a sequence of characters 'h' , 'e' , 'l' , 'l' , and 'o' .

We use single quotes or double quotes to represent a string in Python. For example,

Here, we have created a string variable named string1 . The variable is initialized with the string "Python Programming" .

Example: Python String

In the above example, we have created string-type variables: name and message with values "Python" and "I love Python" respectively.

Here, we have used double quotes to represent strings, but we can use single quotes too.

Access String Characters in Python

We can access the characters in a string in three ways.

Indexing : One way is to treat strings as a list and use index values. For example,
Negative Indexing : Similar to a list, Python allows negative indexing for its strings. For example,
Slicing : Access a range of characters in a string by using the slicing operator colon : . For example,

Note : If we try to access an index out of the range or use numbers other than an integer, we will get errors.

Python Strings are Immutable

In Python, strings are immutable. That means the characters of a string cannot be changed. For example,

However, we can assign the variable name to a new string. For example,

Python Multiline String

We can also create a multiline string in Python. For this, we use triple double quotes """ or triple single quotes ''' . For example,

In the above example, anything inside the enclosing triple quotes is one multiline string.

Python String Operations

Many operations can be performed with strings, which makes it one of the most used data types in Python.

1. Compare Two Strings

We use the == operator to compare two strings. If two strings are equal, the operator returns True . Otherwise, it returns False . For example,

In the above example,

str1 and str2 are not equal. Hence, the result is False .
str1 and str3 are equal. Hence, the result is True .

2. Join Two or More Strings

In Python, we can join (concatenate) two or more strings using the + operator.

In the above example, we have used the + operator to join two strings: greet and name .

Iterate Through a Python String

We can iterate through a string using a for loop . For example,

Python String Length

In Python, we use the len() method to find the length of a string. For example,

String Membership Test

We can test if a substring exists within a string or not, using the keyword in .

Methods of Python String

Besides those mentioned above, there are various string methods present in Python. Here are some of those methods:

Methods	Description
	Converts the string to uppercase
	Converts the string to lowercase
	Returns a tuple
	Replaces substring inside
	Returns the index of the first occurrence of substring
	Removes trailing characters
	Splits string from left
	Checks if string starts with the specified string
	Checks numeric characters
	Returns index of substring

Escape Sequences in Python

The escape sequence is used to escape some of the characters present inside a string.

Suppose we need to include both a double quote and a single quote inside a string,

Since strings are represented by single or double quotes, the compiler will treat "He said, " as a string. Hence, the above code will cause an error.

To solve this issue, we use the escape character \ in Python.

Here is a list of all the escape sequences supported by Python.

Escape Sequence	Description
	Backslash
	Single quote
	Double quote
	ASCII Bell
	ASCII Backspace
	ASCII Formfeed
	ASCII Linefeed
	ASCII Carriage Return
	ASCII Horizontal Tab
	ASCII Vertical Tab
	Character with octal value ooo
	Character with hexadecimal value HH

Python String Formatting (f-Strings)

Python f-Strings makes it easy to print values and variables. For example,

Here, f'{name} is from {country}' is an f-string .

This new formatting syntax is powerful and easy to use. From now on, we will use f-Strings to print strings and variables.

Python str()
Python String Interpolation

Before we wrap up, let’s put your knowledge of Python string to the test! Can you solve the following challenge?

Write a function to double every letter in a string.

For input 'hello' , the return value should be 'hheelllloo' .

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Python TypeError: 'str' object does not support item assignment Solution

Posted in PROGRAMMING LANGUAGE / PYTHON

Vinay Khatri Last updated on September 16, 2024

Table of Content

A Python string is a sequence of characters. The string characters are immutable, which means once we have initialized a string with a sequence of characters, we can not change those characters again. This is because the string is an immutable data type.

Similar to the Python list, the Python string also supports indexing, and we can use the index number of an individual character to access that character. But if we try to change the string's character value using indexing, we would receive the TypeError: 'str' object does not support item assignment Error.

This guide discusses the following string error and its solution in detail. It also demonstrates a common example scenario so that you can solve the following error for yourself. Let's get started with the error statement.

Python Problem: TypeError: 'str' object does not support item assignment

The Error TypeError: 'str' object does not support item assignment occur in a Python program when we try to change any character of an initialized string.

Error example

The following error statement has two sub-statements separated with a colon " : " specifying what is wrong with the program.

TypeError (Exception Type)
'str' object does not support item assignment

1. TypeError

TypeError is a standard Python exception raised by Python when we perform an invalid operation on an unsupported Python data type .

In the above example, we are receiving this Exception because we tried to assign a new value to the first character of the string " message ". And string characters do not support reassigning. That's why Python raised the TypeError exception.

2. 'str' object does not support item assignment

'str' object does not support item assignment statement is the error message, telling us that we are trying to assign a new character value to the string. And string does not support item assignment.

In the above example, we were trying to change the first character of the string message . And for that, we used the assignment operator on the first character message[0] . And because of the immutable nature of the string, we received the error.

There are many ways to solve the above problem, the easiest way is by converting the string into a list using the list() function. Change the first character and change the list back to the string using the join() method.

Common Example Scenario

Now let's discuss an example scenario where many Python learners commit a mistake in the program and encounter this error.

Error Example

Suppose we need to write a program that accepts a username from the user. And we need to filter that username by removing all the numbers and special characters. The end username should contain only the upper or lowercase alphabets characters.

Error Reason

In the above example, we are getting this error because in line 9 we are trying to change the content of the string username using the assignment operator username[index] = "" .

We can use different techniques to solve the above problems and implement the logic. We can convert the username string to a list, filter the list and then convert it into the string.

Now our code runs successfully, and it also converted our entered admin@123 username to a valid username admin .

In this Python tutorial, we learned what is " TypeError: 'str' object does not support item assignment " Error in Python is and how to debug it. Python raises this error when we accidentally try to assign a new character to the string value. Python string is an immutable data structure and it does not support item assignment operation.

If you are getting a similar error in your program, please check your code and try another way to assign the new item or character to the string. If you are stuck in the following error, you can share your code and query in the comment section. We will try to help you in debugging.

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Vinay Khatri I am a Full Stack Developer with a Bachelor's Degree in Computer Science, who also loves to write technical articles that can help fellow developers.

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TypeError: 'src' object does not support item assignment

The assignment str[i] = str[j] is working inconsistently. Please refer to the screenshots and let me know if I am missing something.

We are receiving TypeError: ‘src’ object does not support item assignment

Regards, Praveen. Thank you!

Please don’t use screenshots. Show the code and the traceback as text.

Strings are immutable. You can’t modify a string by trying to change a character within.

You can create a new string with the bits before, the bits after, and whatever you want in between.

Yeah, you cannot assign a string to a variable, and then modify the string, but you can use the string to create a new one and assign that result to the same variable. Borrowing some code from @BowlOfRed above, you can do this:

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Different Forms of Assignment Statements in Python

We use Python assignment statements to assign objects to names. The target of an assignment statement is written on the left side of the equal sign (=), and the object on the right can be an arbitrary expression that computes an object.

There are some important properties of assignment in Python :-

Assignment creates object references instead of copying the objects.
Python creates a variable name the first time when they are assigned a value.
Names must be assigned before being referenced.
There are some operations that perform assignments implicitly.

Assignment statement forms :-

1. Basic form:

This form is the most common form.

2. Tuple assignment:

When we code a tuple on the left side of the =, Python pairs objects on the right side with targets on the left by position and assigns them from left to right. Therefore, the values of x and y are 50 and 100 respectively.

3. List assignment:

This works in the same way as the tuple assignment.

4. Sequence assignment:

In recent version of Python, tuple and list assignment have been generalized into instances of what we now call sequence assignment – any sequence of names can be assigned to any sequence of values, and Python assigns the items one at a time by position.

5. Extended Sequence unpacking:

It allows us to be more flexible in how we select portions of a sequence to assign.

Here, p is matched with the first character in the string on the right and q with the rest. The starred name (*q) is assigned a list, which collects all items in the sequence not assigned to other names.

This is especially handy for a common coding pattern such as splitting a sequence and accessing its front and rest part.

6. Multiple- target assignment:

In this form, Python assigns a reference to the same object (the object which is rightmost) to all the target on the left.

7. Augmented assignment :

The augmented assignment is a shorthand assignment that combines an expression and an assignment.

There are several other augmented assignment forms:

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Python's Assignment Operator: Write Robust Assignments

Table of Contents

The Assignment Statement Syntax

The assignment operator, assignments and variables, other assignment syntax, initializing and updating variables, making multiple variables refer to the same object, updating lists through indices and slices, adding and updating dictionary keys, doing parallel assignments, unpacking iterables, providing default argument values, augmented mathematical assignment operators, augmented assignments for concatenation and repetition, augmented bitwise assignment operators, annotated assignment statements, assignment expressions with the walrus operator, managed attribute assignments, define or call a function, work with classes, import modules and objects, use a decorator, access the control variable in a for loop or a comprehension, use the as keyword, access the _ special variable in an interactive session, built-in objects, named constants.

Python’s assignment operators allow you to define assignment statements . This type of statement lets you create, initialize, and update variables throughout your code. Variables are a fundamental cornerstone in every piece of code, and assignment statements give you complete control over variable creation and mutation.

Learning about the Python assignment operator and its use for writing assignment statements will arm you with powerful tools for writing better and more robust Python code.

In this tutorial, you’ll:

Use Python’s assignment operator to write assignment statements
Take advantage of augmented assignments in Python
Explore assignment variants, like assignment expressions and managed attributes
Become aware of illegal and dangerous assignments in Python

You’ll dive deep into Python’s assignment statements. To get the most out of this tutorial, you should be comfortable with several basic topics, including variables , built-in data types , comprehensions , functions , and Python keywords . Before diving into some of the later sections, you should also be familiar with intermediate topics, such as object-oriented programming , constants , imports , type hints , properties , descriptors , and decorators .

Free Source Code: Click here to download the free assignment operator source code that you’ll use to write assignment statements that allow you to create, initialize, and update variables in your code.

Assignment Statements and the Assignment Operator

One of the most powerful programming language features is the ability to create, access, and mutate variables . In Python, a variable is a name that refers to a concrete value or object, allowing you to reuse that value or object throughout your code.

To create a new variable or to update the value of an existing one in Python, you’ll use an assignment statement . This statement has the following three components:

A left operand, which must be a variable
The assignment operator ( = )
A right operand, which can be a concrete value , an object , or an expression

Here’s how an assignment statement will generally look in Python:

Here, variable represents a generic Python variable, while expression represents any Python object that you can provide as a concrete value—also known as a literal —or an expression that evaluates to a value.

To execute an assignment statement like the above, Python runs the following steps:

Evaluate the right-hand expression to produce a concrete value or object . This value will live at a specific memory address in your computer.
Store the object’s memory address in the left-hand variable . This step creates a new variable if the current one doesn’t already exist or updates the value of an existing variable.

The second step shows that variables work differently in Python than in other programming languages. In Python, variables aren’t containers for objects. Python variables point to a value or object through its memory address. They store memory addresses rather than objects.

This behavior difference directly impacts how data moves around in Python, which is always by reference . In most cases, this difference is irrelevant in your day-to-day coding, but it’s still good to know.

The central component of an assignment statement is the assignment operator . This operator is represented by the = symbol, which separates two operands:

A value or an expression that evaluates to a concrete value

Operators are special symbols that perform mathematical , logical , and bitwise operations in a programming language. The objects (or object) on which an operator operates are called operands .

Unary operators, like the not Boolean operator, operate on a single object or operand, while binary operators act on two. That means the assignment operator is a binary operator.

Note: Like C , Python uses == for equality comparisons and = for assignments. Unlike C, Python doesn’t allow you to accidentally use the assignment operator ( = ) in an equality comparison.

Equality is a symmetrical relationship, and assignment is not. For example, the expression a == 42 is equivalent to 42 == a . In contrast, the statement a = 42 is correct and legal, while 42 = a isn’t allowed. You’ll learn more about illegal assignments later on.

The right-hand operand in an assignment statement can be any Python object, such as a number , list , string , dictionary , or even a user-defined object. It can also be an expression. In the end, expressions always evaluate to concrete objects, which is their return value.

Here are a few examples of assignments in Python:

The first two sample assignments in this code snippet use concrete values, also known as literals , to create and initialize number and greeting . The third example assigns the result of a math expression to the total variable, while the last example uses a Boolean expression.

Note: You can use the built-in id() function to inspect the memory address stored in a given variable.

Here’s a short example of how this function works:

The number in your output represents the memory address stored in number . Through this address, Python can access the content of number , which is the integer 42 in this example.

If you run this code on your computer, then you’ll get a different memory address because this value varies from execution to execution and computer to computer.

Unlike expressions, assignment statements don’t have a return value because their purpose is to make the association between the variable and its value. That’s why the Python interpreter doesn’t issue any output in the above examples.

Now that you know the basics of how to write an assignment statement, it’s time to tackle why you would want to use one.

The assignment statement is the explicit way for you to associate a name with an object in Python. You can use this statement for two main purposes:

Creating and initializing new variables
Updating the values of existing variables

When you use a variable name as the left operand in an assignment statement for the first time, you’re creating a new variable. At the same time, you’re initializing the variable to point to the value of the right operand.

On the other hand, when you use an existing variable in a new assignment, you’re updating or mutating the variable’s value. Strictly speaking, every new assignment will make the variable refer to a new value and stop referring to the old one. Python will garbage-collect all the values that are no longer referenced by any existing variable.

Assignment statements not only assign a value to a variable but also determine the data type of the variable at hand. This additional behavior is another important detail to consider in this kind of statement.

Because Python is a dynamically typed language, successive assignments to a given variable can change the variable’s data type. Changing the data type of a variable during a program’s execution is considered bad practice and highly discouraged. It can lead to subtle bugs that can be difficult to track down.

Unlike in math equations, in Python assignments, the left operand must be a variable rather than an expression or a value. For example, the following construct is illegal, and Python flags it as invalid syntax:

In this example, you have expressions on both sides of the = sign, and this isn’t allowed in Python code. The error message suggests that you may be confusing the equality operator with the assignment one, but that’s not the case. You’re really running an invalid assignment.

To correct this construct and convert it into a valid assignment, you’ll have to do something like the following:

In this code snippet, you first import the sqrt() function from the math module. Then you isolate the hypotenuse variable in the original equation by using the sqrt() function. Now your code works correctly.

Now you know what kind of syntax is invalid. But don’t get the idea that assignment statements are rigid and inflexible. In fact, they offer lots of room for customization, as you’ll learn next.

Python’s assignment statements are pretty flexible and versatile. You can write them in several ways, depending on your specific needs and preferences. Here’s a quick summary of the main ways to write assignments in Python:

Up to this point, you’ve mostly learned about the base assignment syntax in the above code snippet. In the following sections, you’ll learn about multiple, parallel, and augmented assignments. You’ll also learn about assignments with iterable unpacking.

Read on to see the assignment statements in action!

Assignment Statements in Action

You’ll find and use assignment statements everywhere in your Python code. They’re a fundamental part of the language, providing an explicit way to create, initialize, and mutate variables.

You can use assignment statements with plain names, like number or counter . You can also use assignments in more complicated scenarios, such as with:

Qualified attribute names , like user.name
Indices and slices of mutable sequences, like a_list[i] and a_list[i:j]
Dictionary keys , like a_dict[key]

This list isn’t exhaustive. However, it gives you some idea of how flexible these statements are. You can even assign multiple values to an equal number of variables in a single line, commonly known as parallel assignment . Additionally, you can simultaneously assign the values in an iterable to a comma-separated group of variables in what’s known as an iterable unpacking operation.

In the following sections, you’ll dive deeper into all these topics and a few other exciting things that you can do with assignment statements in Python.

The most elementary use case of an assignment statement is to create a new variable and initialize it using a particular value or expression:

All these statements create new variables, assigning them initial values or expressions. For an initial value, you should always use the most sensible and least surprising value that you can think of. For example, initializing a counter to something different from 0 may be confusing and unexpected because counters almost always start having counted no objects.

Updating a variable’s current value or state is another common use case of assignment statements. In Python, assigning a new value to an existing variable doesn’t modify the variable’s current value. Instead, it causes the variable to refer to a different value. The previous value will be garbage-collected if no other variable refers to it.

Consider the following examples:

These examples run two consecutive assignments on the same variable. The first one assigns the string "Hello, World!" to a new variable named greeting .

The second assignment updates the value of greeting by reassigning it the "Hi, Pythonistas!" string. In this example, the original value of greeting —the "Hello, World!" string— is lost and garbage-collected. From this point on, you can’t access the old "Hello, World!" string.

Even though running multiple assignments on the same variable during a program’s execution is common practice, you should use this feature with caution. Changing the value of a variable can make your code difficult to read, understand, and debug. To comprehend the code fully, you’ll have to remember all the places where the variable was changed and the sequential order of those changes.

Because assignments also define the data type of their target variables, it’s also possible for your code to accidentally change the type of a given variable at runtime. A change like this can lead to breaking errors, like AttributeError exceptions. Remember that strings don’t have the same methods and attributes as lists or dictionaries, for example.

In Python, you can make several variables reference the same object in a multiple-assignment line. This can be useful when you want to initialize several similar variables using the same initial value:

In this example, you chain two assignment operators in a single line. This way, your two variables refer to the same initial value of 0 . Note how both variables hold the same memory address, so they point to the same instance of 0 .

When it comes to integer variables, Python exhibits a curious behavior. It provides a numeric interval where multiple assignments behave the same as independent assignments. Consider the following examples:

To create n and m , you use independent assignments. Therefore, they should point to different instances of the number 42 . However, both variables hold the same object, which you confirm by comparing their corresponding memory addresses.

Now check what happens when you use a greater initial value:

Now n and m hold different memory addresses, which means they point to different instances of the integer number 300 . In contrast, when you use multiple assignments, both variables refer to the same object. This tiny difference can save you small bits of memory if you frequently initialize integer variables in your code.

The implicit behavior of making independent assignments point to the same integer number is actually an optimization called interning . It consists of globally caching the most commonly used integer values in day-to-day programming.

Under the hood, Python defines a numeric interval in which interning takes place. That’s the interning interval for integer numbers. You can determine this interval using a small script like the following:

This script helps you determine the interning interval by comparing integer numbers from -10 to 500 . If you run the script from your command line, then you’ll get an output like the following:

This output means that if you use a single number between -5 and 256 to initialize several variables in independent statements, then all these variables will point to the same object, which will help you save small bits of memory in your code.

In contrast, if you use a number that falls outside of the interning interval, then your variables will point to different objects instead. Each of these objects will occupy a different memory spot.

You can use the assignment operator to mutate the value stored at a given index in a Python list. The operator also works with list slices . The syntax to write these types of assignment statements is the following:

In the first construct, expression can return any Python object, including another list. In the second construct, expression must return a series of values as a list, tuple, or any other sequence. You’ll get a TypeError if expression returns a single value.

Note: When creating slice objects, you can use up to three arguments. These arguments are start , stop , and step . They define the number that starts the slice, the number at which the slicing must stop retrieving values, and the step between values.

Here’s an example of updating an individual value in a list:

In this example, you update the value at index 2 using an assignment statement. The original number at that index was 7 , and after the assignment, the number is 3 .

Note: Using indices and the assignment operator to update a value in a tuple or a character in a string isn’t possible because tuples and strings are immutable data types in Python.

Their immutability means that you can’t change their items in place :

You can’t use the assignment operator to change individual items in tuples or strings. These data types are immutable and don’t support item assignments.

It’s important to note that you can’t add new values to a list by using indices that don’t exist in the target list:

In this example, you try to add a new value to the end of numbers by using an index that doesn’t exist. This assignment isn’t allowed because there’s no way to guarantee that new indices will be consecutive. If you ever want to add a single value to the end of a list, then use the .append() method.

If you want to update several consecutive values in a list, then you can use slicing and an assignment statement:

In the first example, you update the letters between indices 1 and 3 without including the letter at 3 . The second example updates the letters from index 3 until the end of the list. Note that this slicing appends a new value to the list because the target slice is shorter than the assigned values.

Also note that the new values were provided through a tuple, which means that this type of assignment allows you to use other types of sequences to update your target list.

The third example updates a single value using a slice where both indices are equal. In this example, the assignment inserts a new item into your target list.

In the final example, you use a step of 2 to replace alternating letters with their lowercase counterparts. This slicing starts at index 1 and runs through the whole list, stepping by two items each time.

Updating the value of an existing key or adding new key-value pairs to a dictionary is another common use case of assignment statements. To do these operations, you can use the following syntax:

The first construct helps you update the current value of an existing key, while the second construct allows you to add a new key-value pair to the dictionary.

For example, to update an existing key, you can do something like this:

In this example, you update the current inventory of oranges in your store using an assignment. The left operand is the existing dictionary key, and the right operand is the desired new value.

While you can’t add new values to a list by assignment, dictionaries do allow you to add new key-value pairs using the assignment operator. In the example below, you add a lemon key to inventory :

In this example, you successfully add a new key-value pair to your inventory with 100 units. This addition is possible because dictionaries don’t have consecutive indices but unique keys, which are safe to add by assignment.

The assignment statement does more than assign the result of a single expression to a single variable. It can also cope nicely with assigning multiple values to multiple variables simultaneously in what’s known as a parallel assignment .

Here’s the general syntax for parallel assignments in Python:

Note that the left side of the statement can be either a tuple or a list of variables. Remember that to create a tuple, you just need a series of comma-separated elements. In this case, these elements must be variables.

The right side of the statement must be a sequence or iterable of values or expressions. In any case, the number of elements in the right operand must match the number of variables on the left. Otherwise, you’ll get a ValueError exception.

In the following example, you compute the two solutions of a quadratic equation using a parallel assignment:

In this example, you first import sqrt() from the math module. Then you initialize the equation’s coefficients in a parallel assignment.

The equation’s solution is computed in another parallel assignment. The left operand contains a tuple of two variables, x1 and x2 . The right operand consists of a tuple of expressions that compute the solutions for the equation. Note how each result is assigned to each variable by position.

A classical use case of parallel assignment is to swap values between variables:

The highlighted line does the magic and swaps the values of previous_value and next_value at the same time. Note that in a programming language that doesn’t support this kind of assignment, you’d have to use a temporary variable to produce the same effect:

In this example, instead of using parallel assignment to swap values between variables, you use a new variable to temporarily store the value of previous_value to avoid losing its reference.

For a concrete example of when you’d need to swap values between variables, say you’re learning how to implement the bubble sort algorithm , and you come up with the following function:

In the highlighted line, you use a parallel assignment to swap values in place if the current value is less than the next value in the input list. To dive deeper into the bubble sort algorithm and into sorting algorithms in general, check out Sorting Algorithms in Python .

You can use assignment statements for iterable unpacking in Python. Unpacking an iterable means assigning its values to a series of variables one by one. The iterable must be the right operand in the assignment, while the variables must be the left operand.

Like in parallel assignments, the variables must come as a tuple or list. The number of variables must match the number of values in the iterable. Alternatively, you can use the unpacking operator ( * ) to grab several values in a variable if the number of variables doesn’t match the iterable length.

Here’s the general syntax for iterable unpacking in Python:

Iterable unpacking is a powerful feature that you can use all around your code. It can help you write more readable and concise code. For example, you may find yourself doing something like this:

Whenever you do something like this in your code, go ahead and replace it with a more readable iterable unpacking using a single and elegant assignment, like in the following code snippet:

The numbers list on the right side contains four values. The assignment operator unpacks these values into the four variables on the left side of the statement. The values in numbers get assigned to variables in the same order that they appear in the iterable. The assignment is done by position.

Note: Because Python sets are also iterables, you can use them in an iterable unpacking operation. However, it won’t be clear which value goes to which variable because sets are unordered data structures.

The above example shows the most common form of iterable unpacking in Python. The main condition for the example to work is that the number of variables matches the number of values in the iterable.

What if you don’t know the iterable length upfront? Will the unpacking work? It’ll work if you use the * operator to pack several values into one of your target variables.

For example, say that you want to unpack the first and second values in numbers into two different variables. Additionally, you would like to pack the rest of the values in a single variable conveniently called rest . In this case, you can use the unpacking operator like in the following code:

In this example, first and second hold the first and second values in numbers , respectively. These values are assigned by position. The * operator packs all the remaining values in the input iterable into rest .

The unpacking operator ( * ) can appear at any position in your series of target variables. However, you can only use one instance of the operator:

The iterable unpacking operator works in any position in your list of variables. Note that you can only use one unpacking operator per assignment. Using more than one unpacking operator isn’t allowed and raises a SyntaxError .

Dropping away unwanted values from the iterable is a common use case for the iterable unpacking operator. Consider the following example:

In Python, if you want to signal that a variable won’t be used, then you use an underscore ( _ ) as the variable’s name. In this example, useful holds the only value that you need to use from the input iterable. The _ variable is a placeholder that guarantees that the unpacking works correctly. You won’t use the values that end up in this disposable variable.

Note: In the example above, if your target iterable is a sequence data type, such as a list or tuple, then it’s best to access its last item directly.

To do this, you can use the -1 index:

Using -1 gives you access to the last item of any sequence data type. In contrast, if you’re dealing with iterators , then you won’t be able to use indices. That’s when the *_ syntax comes to your rescue.

The pattern used in the above example comes in handy when you have a function that returns multiple values, and you only need a few of these values in your code. The os.walk() function may provide a good example of this situation.

This function allows you to iterate over the content of a directory recursively. The function returns a generator object that yields three-item tuples. Each tuple contains the following items:

The path to the current directory as a string
The names of all the immediate subdirectories as a list of strings
The names of all the files in the current directory as a list of strings

Now say that you want to iterate over your home directory and list only the files. You can do something like this:

This code will issue a long output depending on the current content of your home directory. Note that you need to provide a string with the path to your user folder for the example to work. The _ placeholder variable will hold the unwanted data.

In contrast, the filenames variable will hold the list of files in the current directory, which is the data that you need. The code will print the list of filenames. Go ahead and give it a try!

The assignment operator also comes in handy when you need to provide default argument values in your functions and methods. Default argument values allow you to define functions that take arguments with sensible defaults. These defaults allow you to call the function with specific values or to simply rely on the defaults.

As an example, consider the following function:

This function takes one argument, called name . This argument has a sensible default value that’ll be used when you call the function without arguments. To provide this sensible default value, you use an assignment.

Note: According to PEP 8 , the style guide for Python code, you shouldn’t use spaces around the assignment operator when providing default argument values in function definitions.

Here’s how the function works:

If you don’t provide a name during the call to greet() , then the function uses the default value provided in the definition. If you provide a name, then the function uses it instead of the default one.

Up to this point, you’ve learned a lot about the Python assignment operator and how to use it for writing different types of assignment statements. In the following sections, you’ll dive into a great feature of assignment statements in Python. You’ll learn about augmented assignments .

Augmented Assignment Operators in Python

Python supports what are known as augmented assignments . An augmented assignment combines the assignment operator with another operator to make the statement more concise. Most Python math and bitwise operators have an augmented assignment variation that looks something like this:

Note that $ isn’t a valid Python operator. In this example, it’s a placeholder for a generic operator. This statement works as follows:

Evaluate expression to produce a value.
Run the operation defined by the operator that prefixes the = sign, using the previous value of variable and the return value of expression as operands.
Assign the resulting value back to variable .

In practice, an augmented assignment like the above is equivalent to the following statement:

As you can conclude, augmented assignments are syntactic sugar . They provide a shorthand notation for a specific and popular kind of assignment.

For example, say that you need to define a counter variable to count some stuff in your code. You can use the += operator to increment counter by 1 using the following code:

In this example, the += operator, known as augmented addition , adds 1 to the previous value in counter each time you run the statement counter += 1 .

It’s important to note that unlike regular assignments, augmented assignments don’t create new variables. They only allow you to update existing variables. If you use an augmented assignment with an undefined variable, then you get a NameError :

Python evaluates the right side of the statement before assigning the resulting value back to the target variable. In this specific example, when Python tries to compute x + 1 , it finds that x isn’t defined.

Great! You now know that an augmented assignment consists of combining the assignment operator with another operator, like a math or bitwise operator. To continue this discussion, you’ll learn which math operators have an augmented variation in Python.

An equation like x = x + b doesn’t make sense in math. But in programming, a statement like x = x + b is perfectly valid and can be extremely useful. It adds b to x and reassigns the result back to x .

As you already learned, Python provides an operator to shorten x = x + b . Yes, the += operator allows you to write x += b instead. Python also offers augmented assignment operators for most math operators. Here’s a summary:

Operator	Description	Example	Equivalent
	Adds the right operand to the left operand and stores the result in the left operand
	Subtracts the right operand from the left operand and stores the result in the left operand
	Multiplies the right operand with the left operand and stores the result in the left operand
	Divides the left operand by the right operand and stores the result in the left operand
	Performs of the left operand by the right operand and stores the result in the left operand
	Finds the remainder of dividing the left operand by the right operand and stores the result in the left operand
	Raises the left operand to the power of the right operand and stores the result in the left operand

The Example column provides generic examples of how to use the operators in actual code. Note that x must be previously defined for the operators to work correctly. On the other hand, y can be either a concrete value or an expression that returns a value.

Note: The matrix multiplication operator ( @ ) doesn’t support augmented assignments yet.

Consider the following example of matrix multiplication using NumPy arrays:

Note that the exception traceback indicates that the operation isn’t supported yet.

To illustrate how augmented assignment operators work, say that you need to create a function that takes an iterable of numeric values and returns their sum. You can write this function like in the code below:

In this function, you first initialize total to 0 . In each iteration, the loop adds a new number to total using the augmented addition operator ( += ). When the loop terminates, total holds the sum of all the input numbers. Variables like total are known as accumulators . The += operator is typically used to update accumulators.

Note: Computing the sum of a series of numeric values is a common operation in programming. Python provides the built-in sum() function for this specific computation.

Another interesting example of using an augmented assignment is when you need to implement a countdown while loop to reverse an iterable. In this case, you can use the -= operator:

In this example, custom_reversed() is a generator function because it uses yield . Calling the function creates an iterator that yields items from the input iterable in reverse order. To decrement the control variable, index , you use an augmented subtraction statement that subtracts 1 from the variable in every iteration.

Note: Similar to summing the values in an iterable, reversing an iterable is also a common requirement. Python provides the built-in reversed() function for this specific computation, so you don’t have to implement your own. The above example only intends to show the -= operator in action.

Finally, counters are a special type of accumulators that allow you to count objects. Here’s an example of a letter counter:

To create this counter, you use a Python dictionary. The keys store the letters. The values store the counts. Again, to increment the counter, you use an augmented addition.

Counters are so common in programming that Python provides a tool specially designed to facilitate the task of counting. Check out Python’s Counter: The Pythonic Way to Count Objects for a complete guide on how to use this tool.

The += and *= augmented assignment operators also work with sequences , such as lists, tuples, and strings. The += operator performs augmented concatenations , while the *= operator performs augmented repetition .

These operators behave differently with mutable and immutable data types:

Operator	Description	Example
	Runs an augmented concatenation operation on the target sequence. Mutable sequences are updated in place. If the sequence is immutable, then a new sequence is created and assigned back to the target name.
	Adds to itself times. Mutable sequences are updated in place. If the sequence is immutable, then a new sequence is created and assigned back to the target name.

Note that the augmented concatenation operator operates on two sequences, while the augmented repetition operator works on a sequence and an integer number.

Consider the following examples and pay attention to the result of calling the id() function:

Mutable sequences like lists support the += augmented assignment operator through the .__iadd__() method, which performs an in-place addition. This method mutates the underlying list, appending new values to its end.

Note: If the left operand is mutable, then x += y may not be completely equivalent to x = x + y . For example, if you do list_1 = list_1 + list_2 instead of list_1 += list_2 above, then you’ll create a new list instead of mutating the existing one. This may be important if other variables refer to the same list.

Immutable sequences, such as tuples and strings, don’t provide an .__iadd__() method. Therefore, augmented concatenations fall back to the .__add__() method, which doesn’t modify the sequence in place but returns a new sequence.

There’s another difference between mutable and immutable sequences when you use them in an augmented concatenation. Consider the following examples:

With mutable sequences, the data to be concatenated can come as a list, tuple, string, or any other iterable. In contrast, with immutable sequences, the data can only come as objects of the same type. You can concatenate tuples to tuples and strings to strings, for example.

Again, the augmented repetition operator works with a sequence on the left side of the operator and an integer on the right side. This integer value represents the number of repetitions to get in the resulting sequence:

When the *= operator operates on a mutable sequence, it falls back to the .__imul__() method, which performs the operation in place, modifying the underlying sequence. In contrast, if *= operates on an immutable sequence, then .__mul__() is called, returning a new sequence of the same type.

Note: Values of n less than 0 are treated as 0 , which returns an empty sequence of the same data type as the target sequence on the left side of the *= operand.

Note that a_list[0] is a_list[3] returns True . This is because the *= operator doesn’t make a copy of the repeated data. It only reflects the data. This behavior can be a source of issues when you use the operator with mutable values.

For example, say that you want to create a list of lists to represent a matrix, and you need to initialize the list with n empty lists, like in the following code:

In this example, you use the *= operator to populate matrix with three empty lists. Now check out what happens when you try to populate the first sublist in matrix :

The appended values are reflected in the three sublists. This happens because the *= operator doesn’t make copies of the data that you want to repeat. It only reflects the data. Therefore, every sublist in matrix points to the same object and memory address.

If you ever need to initialize a list with a bunch of empty sublists, then use a list comprehension :

This time, when you populate the first sublist of matrix , your changes aren’t propagated to the other sublists. This is because all the sublists are different objects that live in different memory addresses.

Bitwise operators also have their augmented versions. The logic behind them is similar to that of the math operators. The following table summarizes the augmented bitwise operators that Python provides:

Operator	Operation	Example	Equivalent
	Augmented bitwise AND ( )
	Augmented bitwise OR ( )
	Augmented bitwise XOR ( )
	Augmented bitwise right shift
	Augmented bitwise left shift

The augmented bitwise assignment operators perform the intended operation by taking the current value of the left operand as a starting point for the computation. Consider the following example, which uses the & and &= operators:

Programmers who work with high-level languages like Python rarely use bitwise operations in day-to-day coding. However, these types of operations can be useful in some situations.

For example, say that you’re implementing a Unix-style permission system for your users to access a given resource. In this case, you can use the characters "r" for reading, "w" for writing, and "x" for execution permissions, respectively. However, using bit-based permissions could be more memory efficient:

You can assign permissions to your users with the OR bitwise operator or the augmented OR bitwise operator. Finally, you can use the bitwise AND operator to check if a user has a certain permission, as you did in the final two examples.

You’ve learned a lot about augmented assignment operators and statements in this and the previous sections. These operators apply to math, concatenation, repetition, and bitwise operations. Now you’re ready to look at other assignment variants that you can use in your code or find in other developers’ code.

Other Assignment Variants

So far, you’ve learned that Python’s assignment statements and the assignment operator are present in many different scenarios and use cases. Those use cases include variable creation and initialization, parallel assignments, iterable unpacking, augmented assignments, and more.

In the following sections, you’ll learn about a few variants of assignment statements that can be useful in your future coding. You can also find these assignment variants in other developers’ code. So, you should be aware of them and know how they work in practice.

In short, you’ll learn about:

Annotated assignment statements with type hints
Assignment expressions with the walrus operator
Managed attribute assignments with properties and descriptors
Implicit assignments in Python

These topics will take you through several interesting and useful examples that showcase the power of Python’s assignment statements.

PEP 526 introduced a dedicated syntax for variable annotation back in Python 3.6 . The syntax consists of the variable name followed by a colon ( : ) and the variable type:

Even though these statements declare three variables with their corresponding data types, the variables aren’t actually created or initialized. So, for example, you can’t use any of these variables in an augmented assignment statement:

If you try to use one of the previously declared variables in an augmented assignment, then you get a NameError because the annotation syntax doesn’t define the variable. To actually define it, you need to use an assignment.

The good news is that you can use the variable annotation syntax in an assignment statement with the = operator:

The first statement in this example is what you can call an annotated assignment statement in Python. You may ask yourself why you should use type annotations in this type of assignment if everybody can see that counter holds an integer number. You’re right. In this example, the variable type is unambiguous.

However, imagine what would happen if you found a variable initialization like the following:

What would be the data type of each user in users ? If the initialization of users is far away from the definition of the User class, then there’s no quick way to answer this question. To clarify this ambiguity, you can provide the appropriate type hint for users :

Now you’re clearly communicating that users will hold a list of User instances. Using type hints in assignment statements that initialize variables to empty collection data types—such as lists, tuples, or dictionaries—allows you to provide more context about how your code works. This practice will make your code more explicit and less error-prone.

Up to this point, you’ve learned that regular assignment statements with the = operator don’t have a return value. They just create or update variables. Therefore, you can’t use a regular assignment to assign a value to a variable within the context of an expression.

Python 3.8 changed this by introducing a new type of assignment statement through PEP 572 . This new statement is known as an assignment expression or named expression .

Note: Expressions are a special type of statement in Python. Their distinguishing characteristic is that expressions always have a return value, which isn’t the case with all types of statements.

Unlike regular assignments, assignment expressions have a return value, which is why they’re called expressions in the first place. This return value is automatically assigned to a variable. To write an assignment expression, you must use the walrus operator ( := ), which was named for its resemblance to the eyes and tusks of a walrus lying on its side.

The general syntax of an assignment statement is as follows:

This expression looks like a regular assignment. However, instead of using the assignment operator ( = ), it uses the walrus operator ( := ). For the expression to work correctly, the enclosing parentheses are required in most use cases. However, there are certain situations in which these parentheses are superfluous. Either way, they won’t hurt you.

Assignment expressions come in handy when you want to reuse the result of an expression or part of an expression without using a dedicated assignment to grab this value beforehand.

Note: Assignment expressions with the walrus operator have several practical use cases. They also have a few restrictions. For example, they’re illegal in certain contexts, such as lambda functions, parallel assignments, and augmented assignments.

For a deep dive into this special type of assignment, check out The Walrus Operator: Python’s Assignment Expressions .

A particularly handy use case for assignment expressions is when you need to grab the result of an expression used in the context of a conditional statement. For example, say that you need to write a function to compute the mean of a sample of numeric values. Without the walrus operator, you could do something like this:

In this example, the sample size ( n ) is a value that you need to reuse in two different computations. First, you need to check whether the sample has data points or not. Then you need to use the sample size to compute the mean. To be able to reuse n , you wrote a dedicated assignment statement at the beginning of your function to grab the sample size.

You can avoid this extra step by combining it with the first use of the target value, len(sample) , using an assignment expression like the following:

The assignment expression introduced in the conditional computes the sample size and assigns it to n . This way, you guarantee that you have a reference to the sample size to use in further computations.

Because the assignment expression returns the sample size anyway, the conditional can check whether that size equals 0 or not and then take a certain course of action depending on the result of this check. The return statement computes the sample’s mean and sends the result back to the function caller.

Python provides a few tools that allow you to fine-tune the operations behind the assignment of attributes. The attributes that run implicit operations on assignments are commonly referred to as managed attributes .

Properties are the most commonly used tool for providing managed attributes in your classes. However, you can also use descriptors and, in some cases, the .__setitem__() special method.

To understand what fine-tuning the operation behind an assignment means, say that you need a Point class that only allows numeric values for its coordinates, x and y . To write this class, you must set up a validation mechanism to reject non-numeric values. You can use properties to attach the validation functionality on top of x and y .

Here’s how you can write your class:

In Point , you use properties for the .x and .y coordinates. Each property has a getter and a setter method . The getter method returns the attribute at hand. The setter method runs the input validation using a try … except block and the built-in float() function. Then the method assigns the result to the actual attribute.

Here’s how your class works in practice:

When you use a property-based attribute as the left operand in an assignment statement, Python automatically calls the property’s setter method, running any computation from it.

Because both .x and .y are properties, the input validation runs whenever you assign a value to either attribute. In the first example, the input values are valid numbers and the validation passes. In the final example, "one" isn’t a valid numeric value, so the validation fails.

If you look at your Point class, you’ll note that it follows a repetitive pattern, with the getter and setter methods looking quite similar. To avoid this repetition, you can use a descriptor instead of a property.

A descriptor is a class that implements the descriptor protocol , which consists of four special methods :

.__get__() runs when you access the attribute represented by the descriptor.
.__set__() runs when you use the attribute in an assignment statement.
.__delete__() runs when you use the attribute in a del statement.
.__set_name__() sets the attribute’s name, creating a name-aware attribute.

Here’s how your code may look if you use a descriptor to represent the coordinates of your Point class:

You’ve removed repetitive code by defining Coordinate as a descriptor that manages the input validation in a single place. Go ahead and run the following code to try out the new implementation of Point :

Great! The class works as expected. Thanks to the Coordinate descriptor, you now have a more concise and non-repetitive version of your original code.

Another way to fine-tune the operations behind an assignment statement is to provide a custom implementation of .__setitem__() in your class. You’ll use this method in classes representing mutable data collections, such as custom list-like or dictionary-like classes.

As an example, say that you need to create a dictionary-like class that stores its keys in lowercase letters:

In this example, you create a dictionary-like class by subclassing UserDict from collections . Your class implements a .__setitem__() method, which takes key and value as arguments. The method uses str.lower() to convert key into lowercase letters before storing it in the underlying dictionary.

Python implicitly calls .__setitem__() every time you use a key as the left operand in an assignment statement. This behavior allows you to tweak how you process the assignment of keys in your custom dictionary.

Implicit Assignments in Python

Python implicitly runs assignments in many different contexts. In most cases, these implicit assignments are part of the language syntax. In other cases, they support specific behaviors.

Whenever you complete an action in the following list, Python runs an implicit assignment for you:

Define or call a function
Define or instantiate a class
Use the current instance , self
Import modules and objects
Use a decorator
Use the control variable in a for loop or a comprehension
Use the as qualifier in with statements , imports, and try … except blocks
Access the _ special variable in an interactive session

Behind the scenes, Python performs an assignment in every one of the above situations. In the following subsections, you’ll take a tour of all these situations.

When you define a function, the def keyword implicitly assigns a function object to your function’s name. Here’s an example:

From this point on, the name greet refers to a function object that lives at a given memory address in your computer. You can call the function using its name and a pair of parentheses with appropriate arguments. This way, you can reuse greet() wherever you need it.

If you call your greet() function with fellow as an argument, then Python implicitly assigns the input argument value to the name parameter on the function’s definition. The parameter will hold a reference to the input arguments.

When you define a class with the class keyword, you’re assigning a specific name to a class object . You can later use this name to create instances of that class. Consider the following example:

In this example, the name User holds a reference to a class object, which was defined in __main__.User . Like with a function, when you call the class’s constructor with the appropriate arguments to create an instance, Python assigns the arguments to the parameters defined in the class initializer .

Another example of implicit assignments is the current instance of a class, which in Python is called self by convention. This name implicitly gets a reference to the current object whenever you instantiate a class. Thanks to this implicit assignment, you can access .name and .job from within the class without getting a NameError in your code.

Import statements are another variant of implicit assignments in Python. Through an import statement, you assign a name to a module object, class, function, or any other imported object. This name is then created in your current namespace so that you can access it later in your code:

In this example, you import the sys module object from the standard library and assign it to the sys name, which is now available in your namespace, as you can conclude from the second call to the built-in dir() function.

You also run an implicit assignment when you use a decorator in your code. The decorator syntax is just a shortcut for a formal assignment like the following:

Here, you call decorator() with a function object as an argument. This call will typically add functionality on top of the existing function, func() , and return a function object, which is then reassigned to the func name.

The decorator syntax is syntactic sugar for replacing the previous assignment, which you can now write as follows:

Even though this new code looks pretty different from the above assignment, the code implicitly runs the same steps.

Another situation in which Python automatically runs an implicit assignment is when you use a for loop or a comprehension. In both cases, you can have one or more control variables that you then use in the loop or comprehension body:

The memory address of control_variable changes on each iteration of the loop. This is because Python internally reassigns a new value from the loop iterable to the loop control variable on each cycle.

The same behavior appears in comprehensions:

In the end, comprehensions work like for loops but use a more concise syntax. This comprehension creates a new list of strings that mimic the output from the previous example.

The as keyword in with statements, except clauses, and import statements is another example of an implicit assignment in Python. This time, the assignment isn’t completely implicit because the as keyword provides an explicit way to define the target variable.

In a with statement, the target variable that follows the as keyword will hold a reference to the context manager that you’re working with. As an example, say that you have a hello.txt file with the following content:

You want to open this file and print each of its lines on your screen. In this case, you can use the with statement to open the file using the built-in open() function.

In the example below, you accomplish this. You also add some calls to print() that display information about the target variable defined by the as keyword:

This with statement uses the open() function to open hello.txt . The open() function is a context manager that returns a text file object represented by an io.TextIOWrapper instance.

Since you’ve defined a hello target variable with the as keyword, now that variable holds a reference to the file object itself. You confirm this by printing the object and its memory address. Finally, the for loop iterates over the lines and prints this content to the screen.

When it comes to using the as keyword in the context of an except clause, the target variable will contain an exception object if any exception occurs:

In this example, you run a division that raises a ZeroDivisionError . The as keyword assigns the raised exception to error . Note that when you print the exception object, you get only the message because exceptions have a custom .__str__() method that supports this behavior.

There’s a final detail to remember when using the as specifier in a try … except block like the one in the above example. Once you leave the except block, the target variable goes out of scope , and you can’t use it anymore.

Finally, Python’s import statements also support the as keyword. In this context, you can use as to import objects with a different name:

In these examples, you use the as keyword to import the numpy package with the np name and pandas with the name pd . If you call dir() , then you’ll realize that np and pd are now in your namespace. However, the numpy and pandas names are not.

Using the as keyword in your imports comes in handy when you want to use shorter names for your objects or when you need to use different objects that originally had the same name in your code. It’s also useful when you want to make your imported names non-public using a leading underscore, like in import sys as _sys .

The final implicit assignment that you’ll learn about in this tutorial only occurs when you’re using Python in an interactive session. Every time you run a statement that returns a value, the interpreter stores the result in a special variable denoted by a single underscore character ( _ ).

You can access this special variable as you’d access any other variable:

These examples cover several situations in which Python internally uses the _ variable. The first two examples evaluate expressions. Expressions always have a return value, which is automatically assigned to the _ variable every time.

When it comes to function calls, note that if your function returns a fruitful value, then _ will hold it. In contrast, if your function returns None , then the _ variable will remain untouched.

The next example consists of a regular assignment statement. As you already know, regular assignments don’t return any value, so the _ variable isn’t updated after these statements run. Finally, note that accessing a variable in an interactive session returns the value stored in the target variable. This value is then assigned to the _ variable.

Note that since _ is a regular variable, you can use it in other expressions:

In this example, you first create a list of values. Then you call len() to get the number of values in the list. Python automatically stores this value in the _ variable. Finally, you use _ to compute the mean of your list of values.

Now that you’ve learned about some of the implicit assignments that Python runs under the hood, it’s time to dig into a final assignment-related topic. In the following few sections, you’ll learn about some illegal and dangerous assignments that you should be aware of and avoid in your code.

Illegal and Dangerous Assignments in Python

In Python, you’ll find a few situations in which using assignments is either forbidden or dangerous. You must be aware of these special situations and try to avoid them in your code.

In the following sections, you’ll learn when using assignment statements isn’t allowed in Python. You’ll also learn about some situations in which using assignments should be avoided if you want to keep your code consistent and robust.

You can’t use Python keywords as variable names in assignment statements. This kind of assignment is explicitly forbidden. If you try to use a keyword as a variable name in an assignment, then you get a SyntaxError :

Whenever you try to use a keyword as the left operand in an assignment statement, you get a SyntaxError . Keywords are an intrinsic part of the language and can’t be overridden.

If you ever feel the need to name one of your variables using a Python keyword, then you can append an underscore to the name of your variable:

In this example, you’re using the desired name for your variables. Because you added a final underscore to the names, Python doesn’t recognize them as keywords, so it doesn’t raise an error.

Note: Even though adding an underscore at the end of a name is an officially recommended practice , it can be confusing sometimes. Therefore, try to find an alternative name or use a synonym whenever you find yourself using this convention.

For example, you can write something like this:

In this example, using the name booking_class for your variable is way clearer and more descriptive than using class_ .

You’ll also find that you can use only a few keywords as part of the right operand in an assignment statement. Those keywords will generally define simple statements that return a value or object. These include lambda , and , or , not , True , False , None , in , and is . You can also use the for keyword when it’s part of a comprehension and the if keyword when it’s used as part of a ternary operator .

In an assignment, you can never use a compound statement as the right operand. Compound statements are those that require an indented block, such as for and while loops, conditionals, with statements, try … except blocks, and class or function definitions.

Sometimes, you need to name variables, but the desired or ideal name is already taken and used as a built-in name. If this is your case, think harder and find another name. Don’t shadow the built-in.

Shadowing built-in names can cause hard-to-identify problems in your code. A common example of this issue is using list or dict to name user-defined variables. In this case, you override the corresponding built-in names, which won’t work as expected if you use them later in your code.

Consider the following example:

The exception in this example may sound surprising. How come you can’t use list() to build a list from a call to map() that returns a generator of square numbers?

By using the name list to identify your list of numbers, you shadowed the built-in list name. Now that name points to a list object rather than the built-in class. List objects aren’t callable, so your code no longer works.

In Python, you’ll have nothing that warns against using built-in, standard-library, or even relevant third-party names to identify your own variables. Therefore, you should keep an eye out for this practice. It can be a source of hard-to-debug errors.

In programming, a constant refers to a name associated with a value that never changes during a program’s execution. Unlike other programming languages, Python doesn’t have a dedicated syntax for defining constants. This fact implies that Python doesn’t have constants in the strict sense of the word.

Python only has variables. If you need a constant in Python, then you’ll have to define a variable and guarantee that it won’t change during your code’s execution. To do that, you must avoid using that variable as the left operand in an assignment statement.

To tell other Python programmers that a given variable should be treated as a constant, you must write your variable’s name in capital letters with underscores separating the words. This naming convention has been adopted by the Python community and is a recommendation that you’ll find in the Constants section of PEP 8 .

In the following examples, you define some constants in Python:

The problem with these constants is that they’re actually variables. Nothing prevents you from changing their value during your code’s execution. So, at any time, you can do something like the following:

These assignments modify the value of two of your original constants. Python doesn’t complain about these changes, which can cause issues later in your code. As a Python developer, you must guarantee that named constants in your code remain constant.

The only way to do that is never to use named constants in an assignment statement other than the constant definition.

You’ve learned a lot about Python’s assignment operators and how to use them for writing assignment statements . With this type of statement, you can create, initialize, and update variables according to your needs. Now you have the required skills to fully manage the creation and mutation of variables in your Python code.

In this tutorial, you’ve learned how to:

Write assignment statements using Python’s assignment operators
Work with augmented assignments in Python
Explore assignment variants, like assignment expression and managed attributes
Identify illegal and dangerous assignments in Python

Learning about the Python assignment operator and how to use it in assignment statements is a fundamental skill in Python. It empowers you to write reliable and effective Python code.

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Python's Assignment Operator: Write Robust Assignments (Source Code)

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Strings & Input >

Python also includes another method of building strings, which are known as “F-strings”. F-strings allow us to put placeholders in strings that are later replaced with values from variables, effectively creating a way to build “templates” that can be used throughout our program.

The easiest way to see how this works is looking at a few examples. Let’s start with a simple one:

If the user inputs "Willie Wildcat" when prompted, then this code will produce this output:

There are many important parts to this example, so let’s look at each one individually. First, in the print() statement, we see the string "Hello {name}" . This is an example of a template string , which includes a set of curly braces {} as placeholders for data to be inserted. Each template string can have unlimited sets of curly braces. Inside of each set of curly braces, we can place the variable or expression that will be substituted at that location as a string.

Also, we notice that in front of the string, we see the character f . Preceding a string with f outside of the quotation marks will denote the string as an f-string (hence the name), which allows the values inside to be interpolated . Interpolation is the term used when formatting marks in a string, such as the curly braces in an f-string, are interpreted and replaced with the correct values they represent.

Python f-strings can do many powerful things, such as handle more complex formatting and multiple lines. For right now, we’ll just use simple variable placeholders in our f-strings, but over time we’ll introduce additional ways to use f-strings to achieve the desired output.

Formatting Numbers

The most powerful use of f-strings is to insert numerical values directly into strings without having to convert each value directly to the str data type - the interpolation process handles this for us.

For example, we can update our previous program to use f-strings to display the output in a single print() statement, and we can also add additional information with ease:

When we execute this program, we’ll see output that looks like this:

This example shows how easy it is to build complex output strings using f-strings. We can expand the template syntax to even round numbers. f"{.2f}" allows us to format a number to two decimal places. The 2 represents the number of places you want to round to and the ‘f’ inside the curly brackets indicates that you are trying to format the number as a floating point number.

If we add a comma into the template string f"{,.2f}" , we can automatically format in commas for thousands, millions, etc. For example:

Prior to the introduction of f-strings, it was common to use the format() method to place values inside of a template string. The last line of the previous example would look like this using the format method:

As we can see, the format() method receives each value as an argument, and it will replace the curly brace placeholders {} in the template string with each value, working from left to right. The output produced will be identical to the f-string in the example above.

We won’t use the format() method in this class, but you may see it in many online tutorials and documentation since f-strings were introduced relatively recently.

Last modified by: Josh Weese Aug 30, 2024

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Python - Add to a dictionary using a string

[Python 3.4.2] I know this question sounds ridiculous, but I can't figure out where I'm messing up. I'm trying to add keys and values to a dictionary by using strings instead of quoted text. So instead of this,

When I run the command above, I get this error:

I think Python is thinking that I'm trying to create a string, not add to a dictionary. I'm guessing I'm using the wrong syntax. This is what I'm trying to do:

I want this^ command to do this:

I'm getting this error:

I should probably give some more context. I'm:

creating one dictionary
creating a copy of it (because I need to edit the dictionary while iterating through it)
iterating through the first dictionary while running some queries
trying to assign a query's result as a value for each "key: value" in the dictionary.

Here's a picture to show what I mean:

key: value: query_as_new_value

-----EDIT-----

Sorry, I should have clarified: the dictionary's name is not actually 'dict'; I called it 'dict' in my question to show that it was a dictionary.

I'll just post the whole process I'm writing in my script. The error occurs during the last command of the function. Commented out at the very bottom are some other things I've tried.

-----FINAL EDIT-----

Matthias helped me figure it out, although acushner had the solution too. I was trying to make the dictionary three "levels" deep, but Python dictionaries cannot work this way. Instead, I needed to create a nested dictionary. To use an illustration, I was trying to do {key: value: value} when I needed to do {key: {key: value}} .

To apply this to my code, I need to create the [second] dictionary with all three strings at once. So instead of this:

I need to do this:

Thanks a ton for all your help guys!

if key is not defined before you will get error – Hackaholic Commented Dec 3, 2014 at 19:31
Yeah, it's already defined. All three strings ( string_for_key , string_for_value , and string_for_deeper_value ) are already defined. The dictionary already contains the key pointed to by string_for_key and the value pointed to by string_for_key . I'm trying to insert string_for_deeper_value into the dictionary as well. – GreenRaccoon23 Commented Dec 3, 2014 at 19:37

3 Answers 3

You could create a dictionary that expands by itself (Python 3 required).

Use it like this.

Now I'm going to explain your problem with the message TypeError: 'str' object does not support item assignment .

This code will work

data['a'] doesn't exist, so the default value dict is used. Now data['a'] is a dict and this dictionary gets a new value with the key 'b' and the value 'c' .

This code won't work

The value of data['a'] is defined as the string 'c' . Now you can only perform string operations with data['a'] . You can't use it as a dictionary now and that's why data['a']['b'] = 'c' fails.

you don't even need a class for that. dd = lambda: defaultdict(dd) – acushner Commented Dec 3, 2014 at 19:41
1 @acushner: I upvoted your answer because that ist what I would do. My code is just a part from a more complex class and might come handy sometimes. – Matthias Commented Dec 3, 2014 at 19:44
Each of the AutoTree and dd = lambda: defaultdict(dd) options still give me TypeError: list indices must be integers, not str . Thanks for all the help though guys. I think the problem is that I'm using a string instead of text on the right hand side of the equation. So my_dict[key][value] = string instead of my_dict[key][value] = 'text' – GreenRaccoon23 Commented Dec 3, 2014 at 20:29
that is not it. at all. either my_dict is a list or my_dict[key] is a list . that is your problem. – acushner Commented Dec 3, 2014 at 20:43
@GreenRaccoon23: The error TypeError: list indices must be integers, not str has nothing to with the dictionary code. There is no list involved. – Matthias Commented Dec 3, 2014 at 20:46

first, do not use dict as your variable name as it shadows the built-in of the same name.

second, all you want is a nested dictionary, no?

another way, as @Matthias suggested, is to create a bottomless dictionary:

Thanks, I've tried this, but instead of d[string_for_key][string_for_value] = 'snth' I'm using d[string_for_key][string_for_value] = snth . It gives me the error TypeError: list indices must be integers, not str – GreenRaccoon23 Commented Dec 3, 2014 at 19:47
you are creating a list somewhere. check the type of your objects – acushner Commented Dec 3, 2014 at 20:41
Yeah, sorry, I meant TypeError: 'str' object does not support item assignment . I did this in another comment too. :S – GreenRaccoon23 Commented Dec 3, 2014 at 21:05

you can do something like this:

Note: dict is inbuilt don't use it as variable name

Thanks, I've tried this, but I get the error AttributeError: 'dict' object has no attribute 'append' – GreenRaccoon23 Commented Dec 3, 2014 at 19:45
Sure, I added some of my script into my original question. – GreenRaccoon23 Commented Dec 3, 2014 at 20:13

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COMMENTS

Alternative to python string item assignment
Since strings are "immutable", you get the effect of editing by constructing a modified version of the string and assigning it over the old value. If you want to replace or insert to a specific position in the string, the most array-like syntax is to use slices:
TypeError: 'str' object does not support item assignment
The last step is to join the list items into a string with an empty string separator. The str.join() method takes an iterable as an argument and returns a string which is the concatenation of the strings in the iterable.. Python indexes are zero-based, so the first character in a string has an index of 0, and the last character has an index of -1 or len(a_string) - 1.
[Solved] TypeError: 'str' Object Does Not Support Item Assignment
TypeError: 'str' Object Does Not Support Item Assignment in PySpark. Solution; TypeError: 'str' Object Does Not Support Item Assignment in PyMongo. Solution; TypeError: 'str' Object Does Not Support Item Assignment in Random Shuffle. Solution; TypeError: 'str' Object Does Not Support Item Assignment in Pandas Data Frame ...
Python 'str' object does not support item assignment solution
You could also use slicing if you want to create a new string based on parts of an old string. An Example Scenario. We're going to write a program that checks whether a number is in a string. If a number is in a string, it should be replaced with an empty string. This will remove the number. Our program is below:
Fix Python TypeError: 'str' object does not support item assignment
greet[0] = 'J'. TypeError: 'str' object does not support item assignment. To fix this error, you can create a new string with the desired modifications, instead of trying to modify the original string. This can be done by calling the replace() method from the string. See the example below: old_str = 'Hello, world!'.
Python String Error: 'str' Object Does Not Support Item Assignment
When executing this code, the interpreter will raise the Python String Error: 'str' Object Does Not Support Item Assignment. Since strings are immutable in Python, it's impossible to change any individual character in the string object through item assignment.
How to Fix STR Object Does Not Support Item Assignment Error in Python
# String Variable string = "Hello Python" # printing Fourth index element of the String print (string[4]) # Creating list of String elements lst = list (string) print (lst) # Assigning value to the list lst[4] = "a" print (lst) # use join function to convert list into string new_String = "". join(lst) print (new_String)
How to Solve Python TypeError: 'str' object does not support item
Strings are immutable objects which means we cannot change them once created. We have to create a new string object and add the elements we want to that new object. Item assignment changes an object in place, which is only suitable for mutable objects like lists. Item assignment is suitable for lists because they are mutable.
Python TypeError: Str Object Does Not Support Item Assignment
Example: python Create a new string object with the desired value new_string = Hello world! Use a list to store the values you want to assign values = [a, b, c] Skip to content ... What does it mean for an `str` object to not support item assignment? In Python, an `str` object is a sequence of characters. As such, it can be indexed and sliced ...
Python Strings (With Examples)
Python Strings are Immutable. In Python, strings are immutable. That means the characters of a string cannot be changed. For example, ... TypeError: 'str' object does not support item assignment. However, we can assign the variable name to a new string. For example, message = 'Hola Amigos' # assign new string to message variable message ...
How to assign item to a string in python
It would be easier, I think, if you actually broke the string down into a list, where each item in the list was a single letter. Then you could index it the way you wanted. If you wanted to then print it as a word: print(''.join(item for item in my_list)) -
Python String
Output: Initial String: Hello, I'm a Geek Deleting character at 2nd Index: Traceback (most recent call last): File "e:\GFG\Python codes\Codes\demo.py", line 9, in <module> del String1[2] TypeError: 'str' object doesn't support item deletion But using slicing we can remove the character from the original string and store the result in a new string. Example: In this example, we will first slice ...
Python TypeError: 'str' object does not support item assignment Solution
There are many ways to solve the above problem, the easiest way is by converting the string into a list using the list () function. Change the first character and change the list back to the string using the join () method. #string. string = "this is a string" #convert the string to list.
TypeError: 'src' object does not support item assignment
Strings are immutable. You can't modify a string by trying to change a character within. >>> s = "foobar" >>> s[3] = "j" Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'str' object does not support item assignment You can create a new string with the bits before, the bits after, and whatever you want in between.
Different Forms of Assignment Statements in Python
Multiple- target assignment: x = y = 75. print(x, y) In this form, Python assigns a reference to the same object (the object which is rightmost) to all the target on the left. OUTPUT. 75 75. 7. Augmented assignment : The augmented assignment is a shorthand assignment that combines an expression and an assignment.
Python's Assignment Operator: Write Robust Assignments
Here, variable represents a generic Python variable, while expression represents any Python object that you can provide as a concrete value—also known as a literal—or an expression that evaluates to a value. To execute an assignment statement like the above, Python runs the following steps: Evaluate the right-hand expression to produce a concrete value or object.
How to make python class support item assignment?
To avoid inheritance from dict, you can make a class inherit from MutableMapping, and then provide methods for __setitem__ and __getitem__. Additionally, the class will need to support methods for __delitem__, __iter__, __len__, and (optionally) other inherited mixin methods, like pop. The documentation has more info on the details.
TypeError 'str' Object Does Not Support Item Assignment
The Problem Jump To Solution. When you run the code below, Python will throw the runtime exception TypeError: 'str' object does not support item assignment. text = "hello world". if text[0].islower(): text[0] = text[0].upper() This happens because in Python strings are immutable, and can't be changed in place.
Python Assign String Variables
W3Schools offers free online tutorials, references and exercises in all the major languages of the web. Covering popular subjects like HTML, CSS, JavaScript, Python, SQL, Java, and many, many more.
python
Python strings are immutable, you change them by making a copy. The easiest way to do what you want is probably: text = "Z" + text[1:] The text[1:] returns the string in text from position 1 to the end, positions count from 0 so '1' is the second character. edit: You can use the same string slicing technique for any part of the string
F-Strings :: Introduction to Python
Resources Slides Python also includes another method of building strings, which are known as "F-strings". F-strings allow us to put placeholders in strings that are later replaced with values from variables, effectively creating a way to build "templates" that can be used throughout our program. The easiest way to see how this works is looking at a few examples.
Python
TypeError: 'str' object does not support item assignment I think Python is thinking that I'm trying to create a string, not add to a dictionary. I'm guessing I'm using the wrong syntax. This is what I'm trying to do: dict[string_for_key][string_for_value] = string_for_deeper_value I want this^ command to do this: