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Assignment Operators in Python – A Comprehensive Guide

Ever felt confused about assigning values to variables in Python ? Wondering how to simplify operations like addition, subtraction, or even bitwise shifts?

Many of us face these questions when diving into Python programming .

Assignment operators in Python are here to make our lives easier. These operators help us assign values to variables in a clean and efficient way and make our code efficient and compact.

We’ll explore how these operators work and how we can use them to streamline our code.

Basic Assignment Operator

Let’s start with the basics.

The equal sign (=) is the simple assignment operator in Python. It assigns the value on its right to the variable on its left.

In this example:

• We assign the values 10 to a and 5 to b.
• We add a and b and assign the result to c.
• We print the value of c, which is 15.

Augmented Assignment Operators in Python

Now, let’s move on to augmented assignment operators.

These operators combine an operation with an assignment in one step. They make our code more concise and easier to read.

Addition Assignment Operator (+=)

How It Works: This operator would thus add to the right operand and assign the result to the left operand.

Here, a is initially 10.

The ‘+=’ operator adds 5 to a and assigns the result back to a. So, a becomes 15.

Subtraction Assignment Operator (-=)

How It Works: It subtracts the right operand from the left operand and assigns the result to the left operand.

Initially, a is 10.

The ‘-=’ operator subtracts 5 from a and assigns the result back to a. Thus, a becomes 5.

Multiplication Assignment Operator (*=)

How It Works: This is the operator for multiplication of the left operand by the right operand, with the result being assigned to the left operand.

The ‘*=’ operator multiplies a by 5 and assigns the result back to a. Hence, a becomes 50.

Division Assignment Operator (/=)

How It Works: It divides the left operand by the right and assigns the outcome to the left operand.

The ‘/=’ operator divides a by 5 and assigns the result back to a. Thus, a becomes 2.0.

Modulus Assignment Operator (%=)

How It Works: This operator divides the left operand by the right operand and assigns the remainder to the left operand.

The ‘%=’ operator divides a by 3 and assigns the remainder back to a. Therefore, a becomes 1.

Floor Division Assignment Operator (//=)

How It Works: It performs floor division of the left operand by the right operand and, therefore, modifies the value of the left operand.

The ‘//=’ operator divides a by 3 and assigns the floor value back to a. So, a becomes 3.

Exponentiation Assignment Operator (**=)

How It Works: The operator raises the left operand to the power of the right one and puts the result back into the left operand.

Initially, a is 2.

The ‘**=’ operator raises a to the power of 3 and assigns the result back to a. Therefore, a becomes 8.

Bitwise AND Assignment Operator (&=)

How It Works: It performs a bitwise AND operation on the operands and assigns the result to the left operand.

Initially, a is 5 (0101 in binary).

The ‘&=’ operator performs a bitwise AND with 3 (0011 in binary) and assigns the result back to a. Thus, a becomes 1 (0001 in binary).

Bitwise OR Assignment Operator (|=)

How It Works: This operator performs a bitwise OR operation on the operands and assigns the result to the left operand.

The ‘|=’ operator performs a bitwise OR with 3 (0011 in binary) and assigns the result back to a. So, a becomes 7 (0111 in binary).

Bitwise XOR Assignment Operator (^=)

How It Works: It performs a bitwise XOR operation on the operands and assigns the result to the left operand.

The ‘^=’ operator performs a bitwise XOR with 3 (0011 in binary) and assigns the result back to a. Thus, a becomes 6 (0110 in binary).

Bitwise Right Shift Assignment Operator (>>=)

How It Works: This operator performs a bitwise right shift on the left operand and assigns the result to the left operand.

Initially, a is 8 (1000 in binary).

The ‘>>=’ operator right shifts a by 2 and assigns the result back to a. So, a becomes 2 (0010 in binary).

Bitwise Left Shift Assignment Operator (<<=)

How It Works: It performs a bitwise left shift on the left operand and assigns the result to the left operand.

Initially, a is 3 (0011 in binary).

The ‘<<=’ operator left shifts a by 2 and assigns the result back to a. Therefore, a becomes 12 (1100 in binary).

Introducing the Walrus Operator (:=)

Ever wondered if there’s a way to simplify assignments within expressions?

Meet the Walrus Operator.

The Walrus Operator (:=) allows us to assign values to variables as part of an expression. It makes our code more concise and readable.

Imagine you’re iterating over a list and want to process elements until the list becomes short. The Walrus Operator lets us do this efficiently.

• n is assigned the length of a within the while loop condition.
• The loop runs until a has two or fewer elements.
• We reduce our code’s length without sacrificing clarity.

Practical Examples of Assignment Operators

Let’s dive into more practical examples of assignment operators in Python.

These examples will help us see how assignment operators make our code cleaner and more efficient.

Addition Assignment Operator (+=):

• We use the += operator to accumulate the sum of numbers from 0 to 4.

Subtraction Assignment Operator (-=):

• We use the -= operator to update the balance after each withdrawal.

Multiplication Assignment Operator (*=):

Division Assignment Operator (/=):

Modulus Assignment Operator (%=):

Floor Division Assignment Operator (//=):

Exponentiation Assignment Operator (**=):

Bitwise AND Assignment Operator (&=):

Bitwise OR Assignment Operator (|=):

Bitwise XOR Assignment Operator (^=):

Bitwise Right Shift Assignment Operator (>>=):

Bitwise Left Shift Assignment Operator (<<=):

Mastering assignment operators in Python can significantly improve our coding skills. These operators help us write cleaner, more efficient code. In this comprehensive guide, we explored assignment operators in Python, from the basic operator to the more advanced augmented operators and the Walrus Operator.

Whether we’re using simple assignments or the Walrus Operator, understanding these tools is essential. As we practice and apply these operators, our Python programming becomes more intuitive and effective.

• = operator is used for value assignment.
• == does a comparison to check if the two values are equal.
• += operator adds the right operand to the left operand and assigns the result to the left operand.
• + simply adds the operands without assignment.

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Assignment Operators

Add and assign, subtract and assign, multiply and assign, divide and assign, floor divide and assign, exponent and assign, modulo and assign.

For demonstration purposes, let’s use a single variable, num . Initially, we set num to 6. We can apply all of these operators to num and update it accordingly.

Assigning the value of 6 to num results in num being 6.

Expression: num = 6

Adding 3 to num and assigning the result back to num would result in 9.

Expression: num += 3

Subtracting 3 from num and assigning the result back to num would result in 6.

Expression: num -= 3

Multiplying num by 3 and assigning the result back to num would result in 18.

Expression: num *= 3

Dividing num by 3 and assigning the result back to num would result in 6.0 (always a float).

Expression: num /= 3

Performing floor division on num by 3 and assigning the result back to num would result in 2.

Expression: num //= 3

Raising num to the power of 3 and assigning the result back to num would result in 216.

Expression: num **= 3

Calculating the remainder when num is divided by 3 and assigning the result back to num would result in 2.

Expression: num %= 3

We can effectively put this into Python code, and you can experiment with the code yourself! Click the “Run” button to see the output.

The above code is useful when we want to update the same number. We can also use two different numbers and use the assignment operators to apply them on two different values.

• The Roadmap

Python Assignment Operators

In Python, assignment operators play a vital role in assigning values to variables and modifying them efficiently. While the basic assignment operator = is used most often, Python offers several compound operators that combine assignment with arithmetic or bitwise operations, allowing for more concise and expressive code. These operators help streamline code by saving you from repeatedly referencing the same variable. Let’s dive into each of these assignment operators and understand how they work.

Basic Assignment: =

The simplest assignment operator in Python is the = operator. It assigns the value on the right-hand side to the variable on the left. For instance, if you write:

You are assigning the value 5 to the variable x . This operator forms the basis for all other assignment operators.

Add and Assign: +=

The += operator is a shorthand for adding a value to a variable and then assigning the result back to that same variable. Essentially, x += y is the same as writing x = x + y . This helps shorten code, especially when you’re updating a variable multiple times.

For example:

This is both readable and efficient, especially in loops or repetitive calculations.

Subtract and Assign: -=

Similar to += , the -= operator subtracts a value from the variable and assigns the result back to the variable. Instead of writing x = x - value , you can simply use x -= value .

It keeps your code neat while performing subtraction updates.

Multiply and Assign: *=

The *= operator multiplies the variable by a value and reassigns the result back to that variable. It’s a more concise form of x = x * value , making it handy when you need to scale a value repeatedly.

For instance:

This operator shines in scenarios where multiplication is repeatedly applied to a variable.

Divide and Assign: /=

The /= operator divides the variable by the specified value and assigns the quotient back to the variable. It’s equivalent to writing x = x / value , but more compact.

It’s worth noting that division always results in a floating-point number, even if the operands are integers.

Floor Division and Assign: //=

If you need to perform floor division, which gives you the quotient rounded down to the nearest whole number, you can use the //= operator. This is equivalent to x = x // value .

Here’s an example:

This operator is particularly useful when you need integer division results without any remainder.

Modulus and Assign: %=

The %= , or modulus assignment operator, computes the remainder when dividing the variable by a value and assigns that remainder back to the variable. It’s a quick way to express x = x % value .

This is often used in scenarios like cycling through a sequence or checking even/odd numbers.

Exponent and Assign: **=

If you need to raise a variable to a power, you can use the **= operator. It simplifies x = x ** value , where the variable is raised to the power of the value on the right-hand side.

This is especially useful in mathematical applications requiring exponential growth or power operations.

Bitwise AND and Assign: &=

The &= operator performs a bitwise AND operation between the variable and the value, then assigns the result back to the variable. It’s a concise way to write x = x & value , and it’s used mainly in low-level bit manipulation.

Bitwise OR and Assign: |=

Similarly, the |= operator applies a bitwise OR operation between the variable and a value, reassigning the result. It’s shorthand for x = x | value .

This operator is often used in situations where you need to set specific bits in a binary value.

Bitwise XOR and Assign: ^=

The ^= operator performs a bitwise XOR (exclusive OR) operation between the variable and a value, and then assigns the result back to the variable. It’s a compact way to express x = x ^ value .

This operation is frequently used in cryptography and checksum algorithms.

Bitwise Shift Left and Assign: <<=

The <<= operator shifts the bits of a variable to the left by a specified number of positions and assigns the result back to the variable. This is equivalent to writing x = x << value .

Shifting left is often used for multiplication by powers of two in bit-level optimization.

Bitwise Shift Right and Assign: >>=

Finally, the >>= operator shifts the bits of the variable to the right by the given number of positions and reassigns the result. This is shorthand for x = x >> value .

This is useful when performing division by powers of two at the bit level.

Python Assignment Operators: Conclusion

Python’s assignment operators offer a powerful way to update variables concisely while combining arithmetic or bitwise operations. Understanding these operators not only helps in writing more efficient code but also enhances its readability. Whether you’re performing simple arithmetic or diving into bit-level manipulations, Python’s assignment operators provide the flexibility needed to streamline your code.

Happy Coding!

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02 beginner, 03 intermediate, 04 training programs, assignment operators in python, what is an assignment operator in python, types of assignment operators in python, 1. simple python assignment operator (=), example of simple python assignment operator, 2. augmented assignment operators in python, 1. augmented arithmetic assignment operators in python, 2. augmented bitwise assignment operators in python, augmented arithmetic assignment operators in python, 1. augmented addition operator (+=), example of augmented addition operator in python, 2. augmented subtraction operator (-=), example of augmented subtraction operator in python, 3. augmented multiplication operator (*=), example of augmented multiplication operator in python, 4. augmented division operator (/=), example of augmented division operator in python, 5. augmented modulus operator (%=), example of augmented modulus operator in python, 6. augmented floor division operator (//=), example of augmented floor division operator in python, 7. augmented exponent operator (**=), example of augmented exponent operator in python, augmented bitwise assignment operators in python, 1. augmented bitwise and (&=), example of augmented bitwise and operator in python, 2. augmented bitwise or (|=), example of augmented bitwise or operator in python, 3. augmented bitwise xor (^=), example of augmented bitwise xor operator in python, 4. augmented bitwise right shift (>>=), example of augmented bitwise right shift operator in python, 5. augmented bitwise left shift (<<=), example of augmented bitwise left shift operator in python, walrus operator in python, syntax of an assignment expression, example of walrus operator in python, live classes schedule, about author.

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Python Assignment Operator

The = (equal to) symbol is defined as assignment operator in Python. The value of Python expression on its right is assigned to a single variable on its left. The = symbol as in programming in general (and Python in particular) should not be confused with its usage in Mathematics, where it states that the expressions on the either side of the symbol are equal.

Example of Assignment Operator in Python

Consider following Python statements −

At the first instance, at least for somebody new to programming but who knows maths, the statement "a=a+b" looks strange. How could a be equal to "a+b"? However, it needs to be reemphasized that the = symbol is an assignment operator here and not used to show the equality of LHS and RHS.

Because it is an assignment, the expression on right evaluates to 15, the value is assigned to a.

In the statement "a+=b", the two operators "+" and "=" can be combined in a "+=" operator. It is called as add and assign operator. In a single statement, it performs addition of two operands "a" and "b", and result is assigned to operand on left, i.e., "a".

Augmented Assignment Operators in Python

In addition to the simple assignment operator, Python provides few more assignment operators for advanced use. They are called cumulative or augmented assignment operators. In this chapter, we shall learn to use augmented assignment operators defined in Python.

Python has the augmented assignment operators for all arithmetic and comparison operators.

Python augmented assignment operators combines addition and assignment in one statement. Since Python supports mixed arithmetic, the two operands may be of different types. However, the type of left operand changes to the operand of on right, if it is wider.

The += operator is an augmented operator. It is also called cumulative addition operator, as it adds "b" in "a" and assigns the result back to a variable.

The following are the augmented assignment operators in Python:

• Augmented Addition Operator
• Augmented Subtraction Operator
• Augmented Multiplication Operator
• Augmented Division Operator
• Augmented Modulus Operator
• Augmented Exponent Operator
• Augmented Floor division Operator

Augmented Addition Operator (+=)

Following examples will help in understanding how the "+=" operator works −

It will produce the following output −

Augmented Subtraction Operator (-=)

Use -= symbol to perform subtract and assign operations in a single statement. The "a-=b" statement performs "a=a-b" assignment. Operands may be of any number type. Python performs implicit type casting on the object which is narrower in size.

Augmented Multiplication Operator (*=)

The "*=" operator works on similar principle. "a*=b" performs multiply and assign operations, and is equivalent to "a=a*b". In case of augmented multiplication of two complex numbers, the rule of multiplication as discussed in the previous chapter is applicable.

Augmented Division Operator (/=)

The combination symbol "/=" acts as divide and assignment operator, hence "a/=b" is equivalent to "a=a/b". The division operation of int or float operands is float. Division of two complex numbers returns a complex number. Given below are examples of augmented division operator.

Augmented Modulus Operator (%=)

To perform modulus and assignment operation in a single statement, use the %= operator. Like the mod operator, its augmented version also is not supported for complex number.

Augmented Exponent Operator (**=)

The "**=" operator results in computation of "a" raised to "b", and assigning the value back to "a". Given below are some examples −

Augmented Floor division Operator (//=)

For performing floor division and assignment in a single statement, use the "//=" operator. "a//=b" is equivalent to "a=a//b". This operator cannot be used with complex numbers.

Logical Python

Effective Python Tutorials

Python Assignment Operators

Introduction to python assignment operators.

Assignment Operators are used for assigning values to the variables. We can also say that assignment operators are used to assign values to the left-hand side operand. For example, in the below table, we are assigning a value to variable ‘a’, which is the left-side operand.

Assignment Operators

Assignment operator.

Equal to sign ‘=’ is used as an assignment operator. It assigns values of the right-hand side expression to the variable or operand present on the left-hand side.

Assigns value 3 to variable ‘a’.

Addition and Assignment Operator

The addition and assignment operator adds left-side and right-side operands and then the sum is assigned to the left-hand side operand.

Below code is equivalent to:  a = a + 2.

Subtraction and Assignment Operator

The subtraction and assignment operator subtracts the right-side operand from the left-side operand, and then the result is assigned to the left-hand side operand.

Below code is equivalent to:  a = a – 2.

Multiplication and Assignment Operator

The multiplication and assignment operator multiplies the right-side operand with the left-side operand, and then the result is assigned to the left-hand side operand.

Below code is equivalent to:  a = a * 2.

Division and Assignment Operator

The division and assignment operator divides the left-side operand with the right-side operand, and then the result is assigned to the left-hand side operand.

Below code is equivalent to:  a = a / 2.

Modulus and Assignment Operator

The modulus and assignment operator divides the left-side operand with the right-side operand, and then the remainder is assigned to the left-hand side operand.

Below code is equivalent to:  a = a % 3.

Floor Division and Assignment Operator

The floor division and assignment operator divides the left side operand with the right side operand. The result is rounded down to the closest integer value(i.e. floor value) and is assigned to the left-hand side operand.

Below code is equivalent to:  a = a // 3.

Exponential and Assignment Operator

The exponential and assignment operator raises the left-side operand to the power of the right-side operand, and the result is assigned to the left-hand side operand.

Below code is equivalent to:  a = a ** 3.

Bitwise AND and Assignment Operator

Bitwise AND and assignment operator performs bitwise AND operation on both the operands and assign the result to the left-hand side operand.

Below code is equivalent to:  a = a & 3.

Illustration:

Bitwise OR and Assignment Operator

Bitwise OR and assignment operator performs bitwise OR operation on both the operands and assign the result to the left-hand side operand.

Below code is equivalent to:  a = a | 3.

Bitwise XOR and Assignment Operator

Bitwise XOR and assignment operator performs bitwise XOR operation on both the operands and assign the result to the left-hand side operand.

Below code is equivalent to:  a = a ^ 3.

Bitwise Right Shift and Assignment Operator

Bitwise right shift and assignment operator right shifts the left operand by the right operand positions and assigns the result to the left-hand side operand.

Below code is equivalent to:  a = a >> 1.

Bitwise Left Shift and Assignment Operator

Bitwise left shift and assignment operator left shifts the left operand by the right operand positions and assigns the result to the left-hand side operand.

Below code is equivalent to:  a = a << 1.

References:

• Different Assignment operators in Python
• Assignment Operator in Python
• Assignment Expressions

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Python Assignment Operator

• Introduction

Chained Assignment

Shorthand assignment, shorthand assignment operators, playground: assignment operator practice, assignment methods.

All assignment operators are used to assign values to variables. Wait, is there more than one assignment operator? Yes, but they're all quite similar to the ones you've seen. You've used the most common assignment operator, and its symbol is a single equals sign ( = ).

For example, to assign x the value of 10 you type the following:

Different Assignment Methods

You have used this assignment statement before to assign values to variables. Apart from this very common way of using it, a few other situations use the same symbol for slightly different assignments.

You can assign the same value to multiple variables in one swoop by using an assignment chain:

This construct assigns 10 to x , y , and z . Using the chained assignment statement in Python is rare, but if you see it around, now you know what that's about.

Shorthand assignments, on the other hand, are a common occurrence in Python code. This is where the other assignment operators come into play. Shorthand assignments make writing code more efficient and can improve readability---at least once you know about them!

For example, think of a situation where you have a variable x and you want to add 1 to that variable:

This works well and is perfectly fine Python code. However, there is a more concise way of writing the same code using shorthand assignment :

Check out how the second line in these two code snippets is different. You don't need to write the name of the variable x a second time using the shorthand operator += like in the example above.

Both code examples shown achieve the exact same result and are equivalent. The shorthand assignment allows you to use less code to complete the task.

Python comes with a couple of shorthand assignment operators. Some of the most common ones include the following:

These operators are combinations of familiar arithmetic operators with the assignment operator ( = ). You have already used some of Python's arithmetic operators, and you'll learn more about them in the upcoming lesson.

Play around and combine different operators you can think of with the assignment operator below.

• Which ones work and do what you expect them to?
• Which ones don't?

Summary: Python Assignment Operator

• Assignment operators are used to assign values to variables
• Shorthand assignment is the most commonly used in Python
• The table summarizing the assignment operators is provided in the lesson
• Chain Assignment : A method used to assign multiple variables at one
• Shorthand Assignment : A series of short forms for manipulating data

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Augmented Assignment Operators in Python

An assignment operator is an operator that is used to assign some value to a variable. Like normally in Python, we write “ a = 5 “ to assign value 5 to variable ‘a’. Augmented assignment operators have a special role to play in Python programming. It basically combines the functioning of the arithmetic or bitwise operator with the assignment operator. So assume if we need to add 7 to a variable “a” and assign the result back to “a”, then instead of writing normally as “ a = a + 7 “, we can use the augmented assignment operator and write the expression as “ a += 7 “. Here += has combined the functionality of arithmetic addition and assignment.

So, augmented assignment operators provide a short way to perform a binary operation and assigning results back to one of the operands. The way to write an augmented operator is just to write that binary operator and assignment operator together. In Python, we have several different augmented assignment operators like +=, -=, *=, /=, //=, **=, |=, &=, >>=, <<=, %= and ^=. Let’s see their functioning with the help of some exemplar codes:

1. Addition and Assignment (+=): This operator combines the impact of arithmetic addition and assignment. Here,

 a = a + b can be written as a += b

2. Subtraction and Assignment (-=): This operator combines the impact of subtraction and assignment.  

a = a – b can be written as a -= b

Example:  

3. Multiplication and Assignment (*=): This operator combines the functionality of multiplication and assignment.  

a = a * b can be written as a *= b

4. Division and Assignment (/=): This operator has the combined functionality of division and assignment.  

a = a / b can be written as a /= b

5. Floor Division and Assignment (//=): It performs the functioning of floor division and assignment.  

a = a // b can be written as a //= b

6. Modulo and Assignment (%=): This operator combines the impact of the modulo operator and assignment.  

a = a % b can be written as a %= b

7. Power and Assignment (**=): This operator is equivalent to the power and assignment operator together.  

a = a**b can be written as a **= b

8. Bitwise AND & Assignment (&=): This operator combines the impact of the bitwise AND operator and assignment operator. 

a = a & b can be written as a &= b

9. Bitwise OR and Assignment (|=): This operator combines the impact of Bitwise OR and assignment operator.  

a = a | b can be written as a |= b

10. Bitwise XOR and Assignment (^=): This augmented assignment operator combines the functionality of the bitwise XOR operator and assignment operator. 

a = a ^ b can be written as a ^= b

11. Bitwise Left Shift and Assignment (<<=): It puts together the functioning of the bitwise left shift operator and assignment operator.  

a = a << b can be written as a <<= b

12. Bitwise Right Shift and Assignment (>>=): It puts together the functioning of the bitwise right shift operator and assignment operator.  

a = a >> b can be written as a >>= b

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Operators are special symbols that perform operations on variables and values. For example,

Here, + is an operator that adds two numbers: 5 and 6 .

• Types of Python Operators

Here's a list of different types of Python operators that we will learn in this tutorial.

• Arithmetic Operators
• Assignment Operators
• Comparison Operators
• Logical Operators
• Bitwise Operators
• Special Operators

1. Python Arithmetic Operators

Arithmetic operators are used to perform mathematical operations like addition, subtraction, multiplication, etc. For example,

Here, - is an arithmetic operator that subtracts two values or variables.

Example 1: Arithmetic Operators in Python

In the above example, we have used multiple arithmetic operators,

• + to add a and b
• - to subtract b from a
• * to multiply a and b
• / to divide a by b
• // to floor divide a by b
• % to get the remainder
• ** to get a to the power b

2. Python Assignment Operators

Assignment operators are used to assign values to variables. For example,

Here, = is an assignment operator that assigns 5 to x .

Here's a list of different assignment operators available in Python.

Example 2: Assignment Operators

Here, we have used the += operator to assign the sum of a and b to a .

Similarly, we can use any other assignment operators as per our needs.

3. Python Comparison Operators

Comparison operators compare two values/variables and return a boolean result: True or False . For example,

Here, the > comparison operator is used to compare whether a is greater than b or not.

Example 3: Comparison Operators

Note: Comparison operators are used in decision-making and loops . We'll discuss more of the comparison operator and decision-making in later tutorials.

4. Python Logical Operators

Logical operators are used to check whether an expression is True or False . They are used in decision-making. For example,

Here, and is the logical operator AND . Since both a > 2 and b >= 6 are True , the result is True .

Example 4: Logical Operators

Note : Here is the truth table for these logical operators.

5. Python Bitwise operators

Bitwise operators act on operands as if they were strings of binary digits. They operate bit by bit, hence the name.

For example, 2 is 10 in binary, and 7 is 111 .

In the table below: Let x = 10 ( 0000 1010 in binary) and y = 4 ( 0000 0100 in binary)

6. Python Special operators

Python language offers some special types of operators like the identity operator and the membership operator. They are described below with examples.

• Identity operators

In Python, is and is not are used to check if two values are located at the same memory location.

It's important to note that having two variables with equal values doesn't necessarily mean they are identical.

Example 4: Identity operators in Python

Here, we see that x1 and y1 are integers of the same values, so they are equal as well as identical. The same is the case with x2 and y2 (strings).

But x3 and y3 are lists. They are equal but not identical. It is because the interpreter locates them separately in memory, although they are equal.

• Membership operators

In Python, in and not in are the membership operators. They are used to test whether a value or variable is found in a sequence ( string , list , tuple , set and dictionary ).

In a dictionary, we can only test for the presence of a key, not the value.

Example 5: Membership operators in Python

Here, 'H' is in message , but 'hello' is not present in message (remember, Python is case-sensitive).

Similarly, 1 is key, and 'a' is the value in dictionary dict1 . Hence, 'a' in y returns False .

• Precedence and Associativity of operators in Python

Table of Contents

• Introduction
• Python Arithmetic Operators
• Python Assignment Operators
• Python Comparison Operators
• Python Logical Operators
• Python Bitwise operators
• Python Special operators

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

Write a function to split the restaurant bill among friends.

• Take the subtotal of the bill and the number of friends as inputs.
• Calculate the total bill by adding 20% tax to the subtotal and then divide it by the number of friends.
• Return the amount each friend has to pay, rounded off to two decimal places.

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Assignment Operators in Python

The assignment operators in Python are essential for efficiently assigning values to variables. These operators allow you to perform calculations and update the value of variables in a single line of code.

In this article, we will explain how assignment operators work, their variations, and how to use them effectively in your programs.

Table of contents

What are Assignment Operators?

The assignment operators are used to assign values to variables. The most common assignment operator is the equal sign ( = ), which assigns the value on the right to the variable on the left. In addition to the basic assignment operator, Python offers a variety of compound operators that combine arithmetic operations with assignment.

List of Assignment Operators in Python

• Simple assignment ( = ) : Assigns a value to a variable.
• Assignment with addition ( += ) : Adds and assigns the result.
• Assignment with subtraction ( -= ) : Subtracts and assigns the result.
• Assignment with multiplication ( *= ) : Multiplies and assigns the result.
• Assignment with division ( /= ) : Divides and assigns the result as a float.
• Assignment with floor division ( //= ) : Performs a floor division and assigns the result.
• Assignment with modulo ( %= ) : Calculates the modulo and assigns the result.
• Assignment with exponentiation ( **= ) : Raises to the power and assigns the result.

Detailed Explanation of Each Operator with Examples

A) simple assignment ( = ).

The most basic assignment operator is the equal sign ( = ), which simply assigns the value on the right to the variable on the left.

In this case, x has the value of 10 .

b) Assignment with Addition ( += )

The += operator adds the value on the right to the existing value of the variable, and then assigns the result back to the variable.

Explanation :

• The value of x is increased by 3 , so x now contains the new value 8 .

c) Assignment with Subtraction ( -= )

The -= operator subtracts the value on the right from the current value of the variable, and then assigns the result to the variable.

• The value of x is reduced by 4 , so x now has the value 6 .

d) Assignment with Multiplication ( *= )

The operator *= multiplies the value on the right by the value of the variable, and then assigns the result to the variable.

• The value of x is multiplied by 2 , and the new value of x is 8 .

e) Assignment with Division ( /= )

The operator /= divides the current value of the variable by the value on the right and then assigns the result to the variable. The result will be a floating-point number, even if both values are integers.

• x is divided by 2 , and the result is 5.0 (a float).

f) Assignment with Floor Division ( //= )

The operator //= performs an integer division, discarding the decimal part, and then assigns the result to the variable.

• x is divided by 3 , and the integer result is 3 .

g) Assignment with Modulus ( %= )

The operator %= calculates the remainder of the division between the current value and the value on the right, and then assigns the result to the variable.

• 10 divided by 3 leaves a remainder of 1 , so x is assigned the value 1 .

h) Assignment with Exponent ( **= )

The operator **= raises the value of the variable to the power indicated by the value on the right and then assigns the result to the variable.

• x is raised to the power of 3 , resulting in 8 .

Advantages of Using Assignment Operators

Combined assignment operators, such as += and -= , not only simplify the code but can also improve performance since the variable is only evaluated once. This can be useful when working with complex expressions or repeated calculations.

Example of Efficient Use

Imagine you have a variable representing the balance in a bank account, and you need to update the balance several times during the execution of your program:

In this example, the assignment operators simplify the process of updating the balance without the need to repeat the variable saldo in each operation.

Complete Example Using Assignment Operators

Next, we present an example that combines several assignment operators in a simple program:

Explanation of the code:

• First, the discount is applied by subtracting the value of descuento from the initial price.
• Then, a percentage interest is applied to the new value.
• Finally, the program prints the final price.
• «Assignment Operators in Python». programiz.com .
• «Understanding Assignment Operators». tutorialspoint.com .
• «Python Assignment Operators Explained». w3schools.com .
• «Python Arithmetic and Assignment Operators». realpython.com .

The operator += takes the current value of a variable, adds the specified value to the right of the operator, and then assigns the result back to the same variable.

Yes, you can use assignment operators with other data types like strings or lists.

The operator /= performs a standard division and returns a floating-point number, while //= performs an integer division and discards any decimal part of the result.

Using compound assignment operators like += can make your code more compact and readable, as well as optimize performance in certain contexts, such as when working with complex variables.

If you try to use compound assignment operators with incompatible types, Python will raise a TypeError.

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Operators are used to perform operations on variables and values.

In the example below, we use the + operator to add together two values:

Python divides the operators in the following groups:

• Arithmetic operators
• Assignment operators
• Comparison operators
• Logical operators
• Identity operators
• Membership operators
• Bitwise operators

Python Arithmetic Operators

Arithmetic operators are used with numeric values to perform common mathematical operations:

Python Assignment Operators

Assignment operators are used to assign values to variables:

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Python Comparison Operators

Comparison operators are used to compare two values:

Python Logical Operators

Logical operators are used to combine conditional statements:

Python Identity Operators

Identity operators are used to compare the objects, not if they are equal, but if they are actually the same object, with the same memory location:

Python Membership Operators

Membership operators are used to test if a sequence is presented in an object:

Python Bitwise Operators

Bitwise operators are used to compare (binary) numbers:

Operator Precedence

Operator precedence describes the order in which operations are performed.

Parentheses has the highest precedence, meaning that expressions inside parentheses must be evaluated first:

Multiplication * has higher precedence than addition + , and therefor multiplications are evaluated before additions:

The precedence order is described in the table below, starting with the highest precedence at the top:

If two operators have the same precedence, the expression is evaluated from left to right.

Addition + and subtraction - has the same precedence, and therefor we evaluate the expression from left to right:

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What’s New In Python 3.10 ¶

Pablo Galindo Salgado

This article explains the new features in Python 3.10, compared to 3.9. Python 3.10 was released on October 4, 2021. For full details, see the changelog .

Summary – Release highlights ¶

New syntax features:

PEP 634 , Structural Pattern Matching: Specification

PEP 635 , Structural Pattern Matching: Motivation and Rationale

PEP 636 , Structural Pattern Matching: Tutorial

bpo-12782 , Parenthesized context managers are now officially allowed.

New features in the standard library:

PEP 618 , Add Optional Length-Checking To zip.

Interpreter improvements:

PEP 626 , Precise line numbers for debugging and other tools.

New typing features:

PEP 604 , Allow writing union types as X | Y

PEP 612 , Parameter Specification Variables

PEP 613 , Explicit Type Aliases

PEP 647 , User-Defined Type Guards

Important deprecations, removals or restrictions:

PEP 644 , Require OpenSSL 1.1.1 or newer

PEP 632 , Deprecate distutils module.

PEP 623 , Deprecate and prepare for the removal of the wstr member in PyUnicodeObject.

PEP 624 , Remove Py_UNICODE encoder APIs

PEP 597 , Add optional EncodingWarning

New Features ¶

Parenthesized context managers ¶.

Using enclosing parentheses for continuation across multiple lines in context managers is now supported. This allows formatting a long collection of context managers in multiple lines in a similar way as it was previously possible with import statements. For instance, all these examples are now valid:

it is also possible to use a trailing comma at the end of the enclosed group:

This new syntax uses the non LL(1) capacities of the new parser. Check PEP 617 for more details.

(Contributed by Guido van Rossum, Pablo Galindo and Lysandros Nikolaou in bpo-12782 and bpo-40334 .)

Better error messages ¶

Syntaxerrors ¶.

When parsing code that contains unclosed parentheses or brackets the interpreter now includes the location of the unclosed bracket of parentheses instead of displaying SyntaxError: unexpected EOF while parsing or pointing to some incorrect location. For instance, consider the following code (notice the unclosed ‘{‘):

Previous versions of the interpreter reported confusing places as the location of the syntax error:

but in Python 3.10 a more informative error is emitted:

In a similar way, errors involving unclosed string literals (single and triple quoted) now point to the start of the string instead of reporting EOF/EOL.

These improvements are inspired by previous work in the PyPy interpreter.

(Contributed by Pablo Galindo in bpo-42864 and Batuhan Taskaya in bpo-40176 .)

SyntaxError exceptions raised by the interpreter will now highlight the full error range of the expression that constitutes the syntax error itself, instead of just where the problem is detected. In this way, instead of displaying (before Python 3.10):

now Python 3.10 will display the exception as:

This improvement was contributed by Pablo Galindo in bpo-43914 .

A considerable amount of new specialized messages for SyntaxError exceptions have been incorporated. Some of the most notable ones are as follows:

Missing : before blocks:

(Contributed by Pablo Galindo in bpo-42997 .)

Unparenthesised tuples in comprehensions targets:

(Contributed by Pablo Galindo in bpo-43017 .)

Missing commas in collection literals and between expressions:

(Contributed by Pablo Galindo in bpo-43822 .)

Multiple Exception types without parentheses:

(Contributed by Pablo Galindo in bpo-43149 .)

Missing : and values in dictionary literals:

(Contributed by Pablo Galindo in bpo-43823 .)

try blocks without except or finally blocks:

(Contributed by Pablo Galindo in bpo-44305 .)

Usage of = instead of == in comparisons:

(Contributed by Pablo Galindo in bpo-43797 .)

Usage of * in f-strings:

(Contributed by Pablo Galindo in bpo-41064 .)

IndentationErrors ¶

Many IndentationError exceptions now have more context regarding what kind of block was expecting an indentation, including the location of the statement:

AttributeErrors ¶

When printing AttributeError , PyErr_Display() will offer suggestions of similar attribute names in the object that the exception was raised from:

(Contributed by Pablo Galindo in bpo-38530 .)

Notice this won’t work if PyErr_Display() is not called to display the error which can happen if some other custom error display function is used. This is a common scenario in some REPLs like IPython.

NameErrors ¶

When printing NameError raised by the interpreter, PyErr_Display() will offer suggestions of similar variable names in the function that the exception was raised from:

Notice this won’t work if PyErr_Display() is not called to display the error, which can happen if some other custom error display function is used. This is a common scenario in some REPLs like IPython.

PEP 626: Precise line numbers for debugging and other tools ¶

PEP 626 brings more precise and reliable line numbers for debugging, profiling and coverage tools. Tracing events, with the correct line number, are generated for all lines of code executed and only for lines of code that are executed.

The f_lineno attribute of frame objects will always contain the expected line number.

The co_lnotab attribute of code objects is deprecated and will be removed in 3.12. Code that needs to convert from offset to line number should use the new co_lines() method instead.

PEP 634: Structural Pattern Matching ¶

Structural pattern matching has been added in the form of a match statement and case statements of patterns with associated actions. Patterns consist of sequences, mappings, primitive data types as well as class instances. Pattern matching enables programs to extract information from complex data types, branch on the structure of data, and apply specific actions based on different forms of data.

Syntax and operations ¶

The generic syntax of pattern matching is:

A match statement takes an expression and compares its value to successive patterns given as one or more case blocks. Specifically, pattern matching operates by:

using data with type and shape (the subject )

evaluating the subject in the match statement

comparing the subject with each pattern in a case statement from top to bottom until a match is confirmed.

executing the action associated with the pattern of the confirmed match

If an exact match is not confirmed, the last case, a wildcard _ , if provided, will be used as the matching case. If an exact match is not confirmed and a wildcard case does not exist, the entire match block is a no-op.

Declarative approach ¶

Readers may be aware of pattern matching through the simple example of matching a subject (data object) to a literal (pattern) with the switch statement found in C, Java or JavaScript (and many other languages). Often the switch statement is used for comparison of an object/expression with case statements containing literals.

More powerful examples of pattern matching can be found in languages such as Scala and Elixir. With structural pattern matching, the approach is “declarative” and explicitly states the conditions (the patterns) for data to match.

While an “imperative” series of instructions using nested “if” statements could be used to accomplish something similar to structural pattern matching, it is less clear than the “declarative” approach. Instead the “declarative” approach states the conditions to meet for a match and is more readable through its explicit patterns. While structural pattern matching can be used in its simplest form comparing a variable to a literal in a case statement, its true value for Python lies in its handling of the subject’s type and shape.

Simple pattern: match to a literal ¶

Let’s look at this example as pattern matching in its simplest form: a value, the subject, being matched to several literals, the patterns. In the example below, status is the subject of the match statement. The patterns are each of the case statements, where literals represent request status codes. The associated action to the case is executed after a match:

If the above function is passed a status of 418, “I’m a teapot” is returned. If the above function is passed a status of 500, the case statement with _ will match as a wildcard, and “Something’s wrong with the internet” is returned. Note the last block: the variable name, _ , acts as a wildcard and insures the subject will always match. The use of _ is optional.

You can combine several literals in a single pattern using | (“or”):

Behavior without the wildcard ¶

If we modify the above example by removing the last case block, the example becomes:

Without the use of _ in a case statement, a match may not exist. If no match exists, the behavior is a no-op. For example, if status of 500 is passed, a no-op occurs.

Patterns with a literal and variable ¶

Patterns can look like unpacking assignments, and a pattern may be used to bind variables. In this example, a data point can be unpacked to its x-coordinate and y-coordinate:

The first pattern has two literals, (0, 0) , and may be thought of as an extension of the literal pattern shown above. The next two patterns combine a literal and a variable, and the variable binds a value from the subject ( point ). The fourth pattern captures two values, which makes it conceptually similar to the unpacking assignment (x, y) = point .

Patterns and classes ¶

If you are using classes to structure your data, you can use as a pattern the class name followed by an argument list resembling a constructor. This pattern has the ability to capture class attributes into variables:

Patterns with positional parameters ¶

You can use positional parameters with some builtin classes that provide an ordering for their attributes (e.g. dataclasses). You can also define a specific position for attributes in patterns by setting the __match_args__ special attribute in your classes. If it’s set to (“x”, “y”), the following patterns are all equivalent (and all bind the y attribute to the var variable):

Nested patterns ¶

Patterns can be arbitrarily nested. For example, if our data is a short list of points, it could be matched like this:

Complex patterns and the wildcard ¶

To this point, the examples have used _ alone in the last case statement. A wildcard can be used in more complex patterns, such as ('error', code, _) . For example:

In the above case, test_variable will match for (‘error’, code, 100) and (‘error’, code, 800).

We can add an if clause to a pattern, known as a “guard”. If the guard is false, match goes on to try the next case block. Note that value capture happens before the guard is evaluated:

Other Key Features ¶

Several other key features:

Like unpacking assignments, tuple and list patterns have exactly the same meaning and actually match arbitrary sequences. Technically, the subject must be a sequence. Therefore, an important exception is that patterns don’t match iterators. Also, to prevent a common mistake, sequence patterns don’t match strings.

Sequence patterns support wildcards: [x, y, *rest] and (x, y, *rest) work similar to wildcards in unpacking assignments. The name after * may also be _ , so (x, y, *_) matches a sequence of at least two items without binding the remaining items.

Mapping patterns: {"bandwidth": b, "latency": l} captures the "bandwidth" and "latency" values from a dict. Unlike sequence patterns, extra keys are ignored. A wildcard **rest is also supported. (But **_ would be redundant, so is not allowed.)

Subpatterns may be captured using the as keyword:

This binds x1, y1, x2, y2 like you would expect without the as clause, and p2 to the entire second item of the subject.

Most literals are compared by equality. However, the singletons True , False and None are compared by identity.

Named constants may be used in patterns. These named constants must be dotted names to prevent the constant from being interpreted as a capture variable:

For the full specification see PEP 634 . Motivation and rationale are in PEP 635 , and a longer tutorial is in PEP 636 .

Optional EncodingWarning and encoding="locale" option ¶

The default encoding of TextIOWrapper and open() is platform and locale dependent. Since UTF-8 is used on most Unix platforms, omitting encoding option when opening UTF-8 files (e.g. JSON, YAML, TOML, Markdown) is a very common bug. For example:

To find this type of bug, an optional EncodingWarning is added. It is emitted when sys.flags.warn_default_encoding is true and locale-specific default encoding is used.

-X warn_default_encoding option and PYTHONWARNDEFAULTENCODING are added to enable the warning.

See Text Encoding for more information.

New Features Related to Type Hints ¶

This section covers major changes affecting PEP 484 type hints and the typing module.

PEP 604: New Type Union Operator ¶

A new type union operator was introduced which enables the syntax X | Y . This provides a cleaner way of expressing ‘either type X or type Y’ instead of using typing.Union , especially in type hints.

In previous versions of Python, to apply a type hint for functions accepting arguments of multiple types, typing.Union was used:

Type hints can now be written in a more succinct manner:

This new syntax is also accepted as the second argument to isinstance() and issubclass() :

See Union Type and PEP 604 for more details.

(Contributed by Maggie Moss and Philippe Prados in bpo-41428 , with additions by Yurii Karabas and Serhiy Storchaka in bpo-44490 .)

PEP 612: Parameter Specification Variables ¶

Two new options to improve the information provided to static type checkers for PEP 484 ‘s Callable have been added to the typing module.

The first is the parameter specification variable. They are used to forward the parameter types of one callable to another callable – a pattern commonly found in higher order functions and decorators. Examples of usage can be found in typing.ParamSpec . Previously, there was no easy way to type annotate dependency of parameter types in such a precise manner.

The second option is the new Concatenate operator. It’s used in conjunction with parameter specification variables to type annotate a higher order callable which adds or removes parameters of another callable. Examples of usage can be found in typing.Concatenate .

See typing.Callable , typing.ParamSpec , typing.Concatenate , typing.ParamSpecArgs , typing.ParamSpecKwargs , and PEP 612 for more details.

(Contributed by Ken Jin in bpo-41559 , with minor enhancements by Jelle Zijlstra in bpo-43783 . PEP written by Mark Mendoza.)

PEP 613: TypeAlias ¶

PEP 484 introduced the concept of type aliases, only requiring them to be top-level unannotated assignments. This simplicity sometimes made it difficult for type checkers to distinguish between type aliases and ordinary assignments, especially when forward references or invalid types were involved. Compare:

Now the typing module has a special value TypeAlias which lets you declare type aliases more explicitly:

See PEP 613 for more details.

(Contributed by Mikhail Golubev in bpo-41923 .)

PEP 647: User-Defined Type Guards ¶

TypeGuard has been added to the typing module to annotate type guard functions and improve information provided to static type checkers during type narrowing. For more information, please see TypeGuard ‘s documentation, and PEP 647 .

(Contributed by Ken Jin and Guido van Rossum in bpo-43766 . PEP written by Eric Traut.)

Other Language Changes ¶

The int type has a new method int.bit_count() , returning the number of ones in the binary expansion of a given integer, also known as the population count. (Contributed by Niklas Fiekas in bpo-29882 .)

The views returned by dict.keys() , dict.values() and dict.items() now all have a mapping attribute that gives a types.MappingProxyType object wrapping the original dictionary. (Contributed by Dennis Sweeney in bpo-40890 .)

PEP 618 : The zip() function now has an optional strict flag, used to require that all the iterables have an equal length.

Builtin and extension functions that take integer arguments no longer accept Decimal s, Fraction s and other objects that can be converted to integers only with a loss (e.g. that have the __int__() method but do not have the __index__() method). (Contributed by Serhiy Storchaka in bpo-37999 .)

If object.__ipow__() returns NotImplemented , the operator will correctly fall back to object.__pow__() and object.__rpow__() as expected. (Contributed by Alex Shkop in bpo-38302 .)

Assignment expressions can now be used unparenthesized within set literals and set comprehensions, as well as in sequence indexes (but not slices).

Functions have a new __builtins__ attribute which is used to look for builtin symbols when a function is executed, instead of looking into __globals__['__builtins__'] . The attribute is initialized from __globals__["__builtins__"] if it exists, else from the current builtins. (Contributed by Mark Shannon in bpo-42990 .)

Two new builtin functions – aiter() and anext() have been added to provide asynchronous counterparts to iter() and next() , respectively. (Contributed by Joshua Bronson, Daniel Pope, and Justin Wang in bpo-31861 .)

Static methods ( @staticmethod ) and class methods ( @classmethod ) now inherit the method attributes ( __module__ , __name__ , __qualname__ , __doc__ , __annotations__ ) and have a new __wrapped__ attribute. Moreover, static methods are now callable as regular functions. (Contributed by Victor Stinner in bpo-43682 .)

Annotations for complex targets (everything beside simple name targets defined by PEP 526 ) no longer cause any runtime effects with from __future__ import annotations . (Contributed by Batuhan Taskaya in bpo-42737 .)

Class and module objects now lazy-create empty annotations dicts on demand. The annotations dicts are stored in the object’s __dict__ for backwards compatibility. This improves the best practices for working with __annotations__ ; for more information, please see Annotations Best Practices . (Contributed by Larry Hastings in bpo-43901 .)

Annotations consist of yield , yield from , await or named expressions are now forbidden under from __future__ import annotations due to their side effects. (Contributed by Batuhan Taskaya in bpo-42725 .)

Usage of unbound variables, super() and other expressions that might alter the processing of symbol table as annotations are now rendered effectless under from __future__ import annotations . (Contributed by Batuhan Taskaya in bpo-42725 .)

Hashes of NaN values of both float type and decimal.Decimal type now depend on object identity. Formerly, they always hashed to 0 even though NaN values are not equal to one another. This caused potentially quadratic runtime behavior due to excessive hash collisions when creating dictionaries and sets containing multiple NaNs. (Contributed by Raymond Hettinger in bpo-43475 .)

A SyntaxError (instead of a NameError ) will be raised when deleting the __debug__ constant. (Contributed by Donghee Na in bpo-45000 .)

SyntaxError exceptions now have end_lineno and end_offset attributes. They will be None if not determined. (Contributed by Pablo Galindo in bpo-43914 .)

New Modules ¶

Improved modules ¶.

Add missing connect_accepted_socket() method. (Contributed by Alex Grönholm in bpo-41332 .)

Misleading phrase “optional arguments” was replaced with “options” in argparse help. Some tests might require adaptation if they rely on exact output match. (Contributed by Raymond Hettinger in bpo-9694 .)

The index() method of array.array now has optional start and stop parameters. (Contributed by Anders Lorentsen and Zackery Spytz in bpo-31956 .)

asynchat, asyncore, smtpd ¶

These modules have been marked as deprecated in their module documentation since Python 3.6. An import-time DeprecationWarning has now been added to all three of these modules.

Add base64.b32hexencode() and base64.b32hexdecode() to support the Base32 Encoding with Extended Hex Alphabet.

Add clearBreakpoints() to reset all set breakpoints. (Contributed by Irit Katriel in bpo-24160 .)

Added the possibility of providing a key function to the APIs in the bisect module. (Contributed by Raymond Hettinger in bpo-4356 .)

Add a codecs.unregister() function to unregister a codec search function. (Contributed by Hai Shi in bpo-41842 .)

collections.abc ¶

The __args__ of the parameterized generic for collections.abc.Callable are now consistent with typing.Callable . collections.abc.Callable generic now flattens type parameters, similar to what typing.Callable currently does. This means that collections.abc.Callable[[int, str], str] will have __args__ of (int, str, str) ; previously this was ([int, str], str) . To allow this change, types.GenericAlias can now be subclassed, and a subclass will be returned when subscripting the collections.abc.Callable type. Note that a TypeError may be raised for invalid forms of parameterizing collections.abc.Callable which may have passed silently in Python 3.9. (Contributed by Ken Jin in bpo-42195 .)

contextlib ¶

Add a contextlib.aclosing() context manager to safely close async generators and objects representing asynchronously released resources. (Contributed by Joongi Kim and John Belmonte in bpo-41229 .)

Add asynchronous context manager support to contextlib.nullcontext() . (Contributed by Tom Gringauz in bpo-41543 .)

Add AsyncContextDecorator , for supporting usage of async context managers as decorators.

The extended color functions added in ncurses 6.1 will be used transparently by curses.color_content() , curses.init_color() , curses.init_pair() , and curses.pair_content() . A new function, curses.has_extended_color_support() , indicates whether extended color support is provided by the underlying ncurses library. (Contributed by Jeffrey Kintscher and Hans Petter Jansson in bpo-36982 .)

The BUTTON5_* constants are now exposed in the curses module if they are provided by the underlying curses library. (Contributed by Zackery Spytz in bpo-39273 .)

dataclasses ¶

__slots__ ¶.

Added slots parameter in dataclasses.dataclass() decorator. (Contributed by Yurii Karabas in bpo-42269 )

Keyword-only fields ¶

dataclasses now supports fields that are keyword-only in the generated __init__ method. There are a number of ways of specifying keyword-only fields.

You can say that every field is keyword-only:

Both name and birthday are keyword-only parameters to the generated __init__ method.

You can specify keyword-only on a per-field basis:

Here only birthday is keyword-only. If you set kw_only on individual fields, be aware that there are rules about re-ordering fields due to keyword-only fields needing to follow non-keyword-only fields. See the full dataclasses documentation for details.

You can also specify that all fields following a KW_ONLY marker are keyword-only. This will probably be the most common usage:

Here, z and t are keyword-only parameters, while x and y are not. (Contributed by Eric V. Smith in bpo-43532 .)

distutils ¶

The entire distutils package is deprecated, to be removed in Python 3.12. Its functionality for specifying package builds has already been completely replaced by third-party packages setuptools and packaging , and most other commonly used APIs are available elsewhere in the standard library (such as platform , shutil , subprocess or sysconfig ). There are no plans to migrate any other functionality from distutils , and applications that are using other functions should plan to make private copies of the code. Refer to PEP 632 for discussion.

The bdist_wininst command deprecated in Python 3.8 has been removed. The bdist_wheel command is now recommended to distribute binary packages on Windows. (Contributed by Victor Stinner in bpo-42802 .)

When a module does not define __loader__ , fall back to __spec__.loader . (Contributed by Brett Cannon in bpo-42133 .)

encodings ¶

encodings.normalize_encoding() now ignores non-ASCII characters. (Contributed by Hai Shi in bpo-39337 .)

Enum __repr__() now returns enum_name.member_name and __str__() now returns member_name . Stdlib enums available as module constants have a repr() of module_name.member_name . (Contributed by Ethan Furman in bpo-40066 .)

Add enum.StrEnum for enums where all members are strings. (Contributed by Ethan Furman in bpo-41816 .)

fileinput ¶

Add encoding and errors parameters in fileinput.input() and fileinput.FileInput . (Contributed by Inada Naoki in bpo-43712 .)

fileinput.hook_compressed() now returns TextIOWrapper object when mode is “r” and file is compressed, like uncompressed files. (Contributed by Inada Naoki in bpo-5758 .)

faulthandler ¶

The faulthandler module now detects if a fatal error occurs during a garbage collector collection. (Contributed by Victor Stinner in bpo-44466 .)

Add audit hooks for gc.get_objects() , gc.get_referrers() and gc.get_referents() . (Contributed by Pablo Galindo in bpo-43439 .)

Add the root_dir and dir_fd parameters in glob() and iglob() which allow to specify the root directory for searching. (Contributed by Serhiy Storchaka in bpo-38144 .)

The hashlib module requires OpenSSL 1.1.1 or newer. (Contributed by Christian Heimes in PEP 644 and bpo-43669 .)

The hashlib module has preliminary support for OpenSSL 3.0.0. (Contributed by Christian Heimes in bpo-38820 and other issues.)

The pure-Python fallback of pbkdf2_hmac() is deprecated. In the future PBKDF2-HMAC will only be available when Python has been built with OpenSSL support. (Contributed by Christian Heimes in bpo-43880 .)

The hmac module now uses OpenSSL’s HMAC implementation internally. (Contributed by Christian Heimes in bpo-40645 .)

IDLE and idlelib ¶

Make IDLE invoke sys.excepthook() (when started without ‘-n’). User hooks were previously ignored. (Contributed by Ken Hilton in bpo-43008 .)

Rearrange the settings dialog. Split the General tab into Windows and Shell/Ed tabs. Move help sources, which extend the Help menu, to the Extensions tab. Make space for new options and shorten the dialog. The latter makes the dialog better fit small screens. (Contributed by Terry Jan Reedy in bpo-40468 .) Move the indent space setting from the Font tab to the new Windows tab. (Contributed by Mark Roseman and Terry Jan Reedy in bpo-33962 .)

The changes above were backported to a 3.9 maintenance release.

Add a Shell sidebar. Move the primary prompt (‘>>>’) to the sidebar. Add secondary prompts (’…’) to the sidebar. Left click and optional drag selects one or more lines of text, as with the editor line number sidebar. Right click after selecting text lines displays a context menu with ‘copy with prompts’. This zips together prompts from the sidebar with lines from the selected text. This option also appears on the context menu for the text. (Contributed by Tal Einat in bpo-37903 .)

Use spaces instead of tabs to indent interactive code. This makes interactive code entries ‘look right’. Making this feasible was a major motivation for adding the shell sidebar. (Contributed by Terry Jan Reedy in bpo-37892 .)

Highlight the new soft keywords match , case , and _ in pattern-matching statements. However, this highlighting is not perfect and will be incorrect in some rare cases, including some _ -s in case patterns. (Contributed by Tal Einat in bpo-44010 .)

New in 3.10 maintenance releases.

Apply syntax highlighting to .pyi files. (Contributed by Alex Waygood and Terry Jan Reedy in bpo-45447 .)

Include prompts when saving Shell with inputs and outputs. (Contributed by Terry Jan Reedy in gh-95191 .)

importlib.metadata ¶

Feature parity with importlib_metadata 4.6 ( history ).

importlib.metadata entry points now provide a nicer experience for selecting entry points by group and name through a new importlib.metadata.EntryPoints class. See the Compatibility Note in the docs for more info on the deprecation and usage.

Added importlib.metadata.packages_distributions() for resolving top-level Python modules and packages to their importlib.metadata.Distribution .

Add inspect.get_annotations() , which safely computes the annotations defined on an object. It works around the quirks of accessing the annotations on various types of objects, and makes very few assumptions about the object it examines. inspect.get_annotations() can also correctly un-stringize stringized annotations. inspect.get_annotations() is now considered best practice for accessing the annotations dict defined on any Python object; for more information on best practices for working with annotations, please see Annotations Best Practices . Relatedly, inspect.signature() , inspect.Signature.from_callable() , and inspect.Signature.from_function() now call inspect.get_annotations() to retrieve annotations. This means inspect.signature() and inspect.Signature.from_callable() can also now un-stringize stringized annotations. (Contributed by Larry Hastings in bpo-43817 .)

itertools ¶

Add itertools.pairwise() . (Contributed by Raymond Hettinger in bpo-38200 .)

linecache ¶

Add os.cpu_count() support for VxWorks RTOS. (Contributed by Peixing Xin in bpo-41440 .)

Add a new function os.eventfd() and related helpers to wrap the eventfd2 syscall on Linux. (Contributed by Christian Heimes in bpo-41001 .)

Add os.splice() that allows to move data between two file descriptors without copying between kernel address space and user address space, where one of the file descriptors must refer to a pipe. (Contributed by Pablo Galindo in bpo-41625 .)

Add O_EVTONLY , O_FSYNC , O_SYMLINK and O_NOFOLLOW_ANY for macOS. (Contributed by Donghee Na in bpo-43106 .)

os.path.realpath() now accepts a strict keyword-only argument. When set to True , OSError is raised if a path doesn’t exist or a symlink loop is encountered. (Contributed by Barney Gale in bpo-43757 .)

Add slice support to PurePath.parents . (Contributed by Joshua Cannon in bpo-35498 .)

Add negative indexing support to PurePath.parents . (Contributed by Yaroslav Pankovych in bpo-21041 .)

Add Path.hardlink_to method that supersedes link_to() . The new method has the same argument order as symlink_to() . (Contributed by Barney Gale in bpo-39950 .)

pathlib.Path.stat() and chmod() now accept a follow_symlinks keyword-only argument for consistency with corresponding functions in the os module. (Contributed by Barney Gale in bpo-39906 .)

Add platform.freedesktop_os_release() to retrieve operation system identification from freedesktop.org os-release standard file. (Contributed by Christian Heimes in bpo-28468 .)

pprint.pprint() now accepts a new underscore_numbers keyword argument. (Contributed by sblondon in bpo-42914 .)

pprint can now pretty-print dataclasses.dataclass instances. (Contributed by Lewis Gaul in bpo-43080 .)

py_compile ¶

Add --quiet option to command-line interface of py_compile . (Contributed by Gregory Schevchenko in bpo-38731 .)

Add an end_lineno attribute to the Function and Class objects in the tree returned by pyclbr.readmodule() and pyclbr.readmodule_ex() . It matches the existing (start) lineno . (Contributed by Aviral Srivastava in bpo-38307 .)

The shelve module now uses pickle.DEFAULT_PROTOCOL by default instead of pickle protocol 3 when creating shelves. (Contributed by Zackery Spytz in bpo-34204 .)

statistics ¶

Add covariance() , Pearson’s correlation() , and simple linear_regression() functions. (Contributed by Tymoteusz Wołodźko in bpo-38490 .)

The exception socket.timeout is now an alias of TimeoutError . (Contributed by Christian Heimes in bpo-42413 .)

Add option to create MPTCP sockets with IPPROTO_MPTCP (Contributed by Rui Cunha in bpo-43571 .)

Add IP_RECVTOS option to receive the type of service (ToS) or DSCP/ECN fields (Contributed by Georg Sauthoff in bpo-44077 .)

The ssl module requires OpenSSL 1.1.1 or newer. (Contributed by Christian Heimes in PEP 644 and bpo-43669 .)

The ssl module has preliminary support for OpenSSL 3.0.0 and new option OP_IGNORE_UNEXPECTED_EOF . (Contributed by Christian Heimes in bpo-38820 , bpo-43794 , bpo-43788 , bpo-43791 , bpo-43799 , bpo-43920 , bpo-43789 , and bpo-43811 .)

Deprecated function and use of deprecated constants now result in a DeprecationWarning . ssl.SSLContext.options has OP_NO_SSLv2 and OP_NO_SSLv3 set by default and therefore cannot warn about setting the flag again. The deprecation section has a list of deprecated features. (Contributed by Christian Heimes in bpo-43880 .)

The ssl module now has more secure default settings. Ciphers without forward secrecy or SHA-1 MAC are disabled by default. Security level 2 prohibits weak RSA, DH, and ECC keys with less than 112 bits of security. SSLContext defaults to minimum protocol version TLS 1.2. Settings are based on Hynek Schlawack’s research. (Contributed by Christian Heimes in bpo-43998 .)

The deprecated protocols SSL 3.0, TLS 1.0, and TLS 1.1 are no longer officially supported. Python does not block them actively. However OpenSSL build options, distro configurations, vendor patches, and cipher suites may prevent a successful handshake.

Add a timeout parameter to the ssl.get_server_certificate() function. (Contributed by Zackery Spytz in bpo-31870 .)

The ssl module uses heap-types and multi-phase initialization. (Contributed by Christian Heimes in bpo-42333 .)

A new verify flag VERIFY_X509_PARTIAL_CHAIN has been added. (Contributed by l0x in bpo-40849 .)

Add audit events for connect/handle() , enable_load_extension() , and load_extension() . (Contributed by Erlend E. Aasland in bpo-43762 .)

Add sys.orig_argv attribute: the list of the original command line arguments passed to the Python executable. (Contributed by Victor Stinner in bpo-23427 .)

Add sys.stdlib_module_names , containing the list of the standard library module names. (Contributed by Victor Stinner in bpo-42955 .)

_thread.interrupt_main() now takes an optional signal number to simulate (the default is still signal.SIGINT ). (Contributed by Antoine Pitrou in bpo-43356 .)

threading ¶

Add threading.gettrace() and threading.getprofile() to retrieve the functions set by threading.settrace() and threading.setprofile() respectively. (Contributed by Mario Corchero in bpo-42251 .)

Add threading.__excepthook__ to allow retrieving the original value of threading.excepthook() in case it is set to a broken or a different value. (Contributed by Mario Corchero in bpo-42308 .)

traceback ¶

The format_exception() , format_exception_only() , and print_exception() functions can now take an exception object as a positional-only argument. (Contributed by Zackery Spytz and Matthias Bussonnier in bpo-26389 .)

Reintroduce the types.EllipsisType , types.NoneType and types.NotImplementedType classes, providing a new set of types readily interpretable by type checkers. (Contributed by Bas van Beek in bpo-41810 .)

For major changes, see New Features Related to Type Hints .

The behavior of typing.Literal was changed to conform with PEP 586 and to match the behavior of static type checkers specified in the PEP.

Literal now de-duplicates parameters.

Equality comparisons between Literal objects are now order independent.

Literal comparisons now respect types. For example, Literal[0] == Literal[False] previously evaluated to True . It is now False . To support this change, the internally used type cache now supports differentiating types.

Literal objects will now raise a TypeError exception during equality comparisons if any of their parameters are not hashable . Note that declaring Literal with unhashable parameters will not throw an error:

(Contributed by Yurii Karabas in bpo-42345 .)

Add new function typing.is_typeddict() to introspect if an annotation is a typing.TypedDict . (Contributed by Patrick Reader in bpo-41792 .)

Subclasses of typing.Protocol which only have data variables declared will now raise a TypeError when checked with isinstance unless they are decorated with runtime_checkable() . Previously, these checks passed silently. Users should decorate their subclasses with the runtime_checkable() decorator if they want runtime protocols. (Contributed by Yurii Karabas in bpo-38908 .)

Importing from the typing.io and typing.re submodules will now emit DeprecationWarning . These submodules have been deprecated since Python 3.8 and will be removed in a future version of Python. Anything belonging to those submodules should be imported directly from typing instead. (Contributed by Sebastian Rittau in bpo-38291 .)

Add new method assertNoLogs() to complement the existing assertLogs() . (Contributed by Kit Yan Choi in bpo-39385 .)

urllib.parse ¶

Python versions earlier than Python 3.10 allowed using both ; and & as query parameter separators in urllib.parse.parse_qs() and urllib.parse.parse_qsl() . Due to security concerns, and to conform with newer W3C recommendations, this has been changed to allow only a single separator key, with & as the default. This change also affects cgi.parse() and cgi.parse_multipart() as they use the affected functions internally. For more details, please see their respective documentation. (Contributed by Adam Goldschmidt, Senthil Kumaran and Ken Jin in bpo-42967 .)

The presence of newline or tab characters in parts of a URL allows for some forms of attacks. Following the WHATWG specification that updates RFC 3986 , ASCII newline \n , \r and tab \t characters are stripped from the URL by the parser in urllib.parse preventing such attacks. The removal characters are controlled by a new module level variable urllib.parse._UNSAFE_URL_BYTES_TO_REMOVE . (See gh-88048 )

Add a LexicalHandler class to the xml.sax.handler module. (Contributed by Jonathan Gossage and Zackery Spytz in bpo-35018 .)

zipimport ¶

Add methods related to PEP 451 : find_spec() , zipimport.zipimporter.create_module() , and zipimport.zipimporter.exec_module() . (Contributed by Brett Cannon in bpo-42131 .)

Add invalidate_caches() method. (Contributed by Desmond Cheong in bpo-14678 .)

Optimizations ¶

Constructors str() , bytes() and bytearray() are now faster (around 30–40% for small objects). (Contributed by Serhiy Storchaka in bpo-41334 .)

The runpy module now imports fewer modules. The python3 -m module-name command startup time is 1.4x faster in average. On Linux, python3 -I -m module-name imports 69 modules on Python 3.9, whereas it only imports 51 modules (-18) on Python 3.10. (Contributed by Victor Stinner in bpo-41006 and bpo-41718 .)

The LOAD_ATTR instruction now uses new “per opcode cache” mechanism. It is about 36% faster now for regular attributes and 44% faster for slots. (Contributed by Pablo Galindo and Yury Selivanov in bpo-42093 and Guido van Rossum in bpo-42927 , based on ideas implemented originally in PyPy and MicroPython.)

When building Python with --enable-optimizations now -fno-semantic-interposition is added to both the compile and link line. This speeds builds of the Python interpreter created with --enable-shared with gcc by up to 30%. See this article for more details. (Contributed by Victor Stinner and Pablo Galindo in bpo-38980 .)

Use a new output buffer management code for bz2 / lzma / zlib modules, and add .readall() function to _compression.DecompressReader class. bz2 decompression is now 1.09x ~ 1.17x faster, lzma decompression 1.20x ~ 1.32x faster, GzipFile.read(-1) 1.11x ~ 1.18x faster. (Contributed by Ma Lin, reviewed by Gregory P. Smith, in bpo-41486 )

When using stringized annotations, annotations dicts for functions are no longer created when the function is created. Instead, they are stored as a tuple of strings, and the function object lazily converts this into the annotations dict on demand. This optimization cuts the CPU time needed to define an annotated function by half. (Contributed by Yurii Karabas and Inada Naoki in bpo-42202 .)

Substring search functions such as str1 in str2 and str2.find(str1) now sometimes use Crochemore & Perrin’s “Two-Way” string searching algorithm to avoid quadratic behavior on long strings. (Contributed by Dennis Sweeney in bpo-41972 )

Add micro-optimizations to _PyType_Lookup() to improve type attribute cache lookup performance in the common case of cache hits. This makes the interpreter 1.04 times faster on average. (Contributed by Dino Viehland in bpo-43452 .)

The following built-in functions now support the faster PEP 590 vectorcall calling convention: map() , filter() , reversed() , bool() and float() . (Contributed by Donghee Na and Jeroen Demeyer in bpo-43575 , bpo-43287 , bpo-41922 , bpo-41873 and bpo-41870 .)

BZ2File performance is improved by removing internal RLock . This makes BZ2File thread unsafe in the face of multiple simultaneous readers or writers, just like its equivalent classes in gzip and lzma have always been. (Contributed by Inada Naoki in bpo-43785 .)

Deprecated ¶

Currently Python accepts numeric literals immediately followed by keywords, for example 0in x , 1or x , 0if 1else 2 . It allows confusing and ambiguous expressions like [0x1for x in y] (which can be interpreted as [0x1 for x in y] or [0x1f or x in y] ). Starting in this release, a deprecation warning is raised if the numeric literal is immediately followed by one of keywords and , else , for , if , in , is and or . In future releases it will be changed to syntax warning, and finally to syntax error. (Contributed by Serhiy Storchaka in bpo-43833 .)

Starting in this release, there will be a concerted effort to begin cleaning up old import semantics that were kept for Python 2.7 compatibility. Specifically, find_loader() / find_module() (superseded by find_spec() ), load_module() (superseded by exec_module() ), module_repr() (which the import system takes care of for you), the __package__ attribute (superseded by __spec__.parent ), the __loader__ attribute (superseded by __spec__.loader ), and the __cached__ attribute (superseded by __spec__.cached ) will slowly be removed (as well as other classes and methods in importlib ). ImportWarning and/or DeprecationWarning will be raised as appropriate to help identify code which needs updating during this transition.

The entire distutils namespace is deprecated, to be removed in Python 3.12. Refer to the module changes section for more information.

Non-integer arguments to random.randrange() are deprecated. The ValueError is deprecated in favor of a TypeError . (Contributed by Serhiy Storchaka and Raymond Hettinger in bpo-37319 .)

The various load_module() methods of importlib have been documented as deprecated since Python 3.6, but will now also trigger a DeprecationWarning . Use exec_module() instead. (Contributed by Brett Cannon in bpo-26131 .)

zimport.zipimporter.load_module() has been deprecated in preference for exec_module() . (Contributed by Brett Cannon in bpo-26131 .)

The use of load_module() by the import system now triggers an ImportWarning as exec_module() is preferred. (Contributed by Brett Cannon in bpo-26131 .)

The use of importlib.abc.MetaPathFinder.find_module() and importlib.abc.PathEntryFinder.find_module() by the import system now trigger an ImportWarning as importlib.abc.MetaPathFinder.find_spec() and importlib.abc.PathEntryFinder.find_spec() are preferred, respectively. You can use importlib.util.spec_from_loader() to help in porting. (Contributed by Brett Cannon in bpo-42134 .)

The use of importlib.abc.PathEntryFinder.find_loader() by the import system now triggers an ImportWarning as importlib.abc.PathEntryFinder.find_spec() is preferred. You can use importlib.util.spec_from_loader() to help in porting. (Contributed by Brett Cannon in bpo-43672 .)

The various implementations of importlib.abc.MetaPathFinder.find_module() ( importlib.machinery.BuiltinImporter.find_module() , importlib.machinery.FrozenImporter.find_module() , importlib.machinery.WindowsRegistryFinder.find_module() , importlib.machinery.PathFinder.find_module() , importlib.abc.MetaPathFinder.find_module() ), importlib.abc.PathEntryFinder.find_module() ( importlib.machinery.FileFinder.find_module() ), and importlib.abc.PathEntryFinder.find_loader() ( importlib.machinery.FileFinder.find_loader() ) now raise DeprecationWarning and are slated for removal in Python 3.12 (previously they were documented as deprecated in Python 3.4). (Contributed by Brett Cannon in bpo-42135 .)

importlib.abc.Finder is deprecated (including its sole method, find_module() ). Both importlib.abc.MetaPathFinder and importlib.abc.PathEntryFinder no longer inherit from the class. Users should inherit from one of these two classes as appropriate instead. (Contributed by Brett Cannon in bpo-42135 .)

The deprecations of imp , importlib.find_loader() , importlib.util.set_package_wrapper() , importlib.util.set_loader_wrapper() , importlib.util.module_for_loader() , pkgutil.ImpImporter , and pkgutil.ImpLoader have all been updated to list Python 3.12 as the slated version of removal (they began raising DeprecationWarning in previous versions of Python). (Contributed by Brett Cannon in bpo-43720 .)

The import system now uses the __spec__ attribute on modules before falling back on module_repr() for a module’s __repr__() method. Removal of the use of module_repr() is scheduled for Python 3.12. (Contributed by Brett Cannon in bpo-42137 .)

importlib.abc.Loader.module_repr() , importlib.machinery.FrozenLoader.module_repr() , and importlib.machinery.BuiltinLoader.module_repr() are deprecated and slated for removal in Python 3.12. (Contributed by Brett Cannon in bpo-42136 .)

sqlite3.OptimizedUnicode has been undocumented and obsolete since Python 3.3, when it was made an alias to str . It is now deprecated, scheduled for removal in Python 3.12. (Contributed by Erlend E. Aasland in bpo-42264 .)

The undocumented built-in function sqlite3.enable_shared_cache is now deprecated, scheduled for removal in Python 3.12. Its use is strongly discouraged by the SQLite3 documentation. See the SQLite3 docs for more details. If a shared cache must be used, open the database in URI mode using the cache=shared query parameter. (Contributed by Erlend E. Aasland in bpo-24464 .)

The following threading methods are now deprecated:

threading.currentThread => threading.current_thread()

threading.activeCount => threading.active_count()

threading.Condition.notifyAll => threading.Condition.notify_all()

threading.Event.isSet => threading.Event.is_set()

threading.Thread.setName => threading.Thread.name

threading.thread.getName => threading.Thread.name

threading.Thread.isDaemon => threading.Thread.daemon

threading.Thread.setDaemon => threading.Thread.daemon

(Contributed by Jelle Zijlstra in gh-87889 .)

pathlib.Path.link_to() is deprecated and slated for removal in Python 3.12. Use pathlib.Path.hardlink_to() instead. (Contributed by Barney Gale in bpo-39950 .)

cgi.log() is deprecated and slated for removal in Python 3.12. (Contributed by Inada Naoki in bpo-41139 .)

The following ssl features have been deprecated since Python 3.6, Python 3.7, or OpenSSL 1.1.0 and will be removed in 3.11:

OP_NO_SSLv2 , OP_NO_SSLv3 , OP_NO_TLSv1 , OP_NO_TLSv1_1 , OP_NO_TLSv1_2 , and OP_NO_TLSv1_3 are replaced by minimum_version and maximum_version .

PROTOCOL_SSLv2 , PROTOCOL_SSLv3 , PROTOCOL_SSLv23 , PROTOCOL_TLSv1 , PROTOCOL_TLSv1_1 , PROTOCOL_TLSv1_2 , and PROTOCOL_TLS are deprecated in favor of PROTOCOL_TLS_CLIENT and PROTOCOL_TLS_SERVER

wrap_socket() is replaced by ssl.SSLContext.wrap_socket()

match_hostname()

RAND_pseudo_bytes() , RAND_egd()

NPN features like ssl.SSLSocket.selected_npn_protocol() and ssl.SSLContext.set_npn_protocols() are replaced by ALPN.

The threading debug ( PYTHONTHREADDEBUG environment variable) is deprecated in Python 3.10 and will be removed in Python 3.12. This feature requires a debug build of Python . (Contributed by Victor Stinner in bpo-44584 .)

Importing from the typing.io and typing.re submodules will now emit DeprecationWarning . These submodules will be removed in a future version of Python. Anything belonging to these submodules should be imported directly from typing instead. (Contributed by Sebastian Rittau in bpo-38291 .)

Removed special methods __int__ , __float__ , __floordiv__ , __mod__ , __divmod__ , __rfloordiv__ , __rmod__ and __rdivmod__ of the complex class. They always raised a TypeError . (Contributed by Serhiy Storchaka in bpo-41974 .)

The ParserBase.error() method from the private and undocumented _markupbase module has been removed. html.parser.HTMLParser is the only subclass of ParserBase and its error() implementation was already removed in Python 3.5. (Contributed by Berker Peksag in bpo-31844 .)

Removed the unicodedata.ucnhash_CAPI attribute which was an internal PyCapsule object. The related private _PyUnicode_Name_CAPI structure was moved to the internal C API. (Contributed by Victor Stinner in bpo-42157 .)

Removed the parser module, which was deprecated in 3.9 due to the switch to the new PEG parser, as well as all the C source and header files that were only being used by the old parser, including node.h , parser.h , graminit.h and grammar.h .

Removed the Public C API functions PyParser_SimpleParseStringFlags , PyParser_SimpleParseStringFlagsFilename , PyParser_SimpleParseFileFlags and PyNode_Compile that were deprecated in 3.9 due to the switch to the new PEG parser.

Removed the formatter module, which was deprecated in Python 3.4. It is somewhat obsolete, little used, and not tested. It was originally scheduled to be removed in Python 3.6, but such removals were delayed until after Python 2.7 EOL. Existing users should copy whatever classes they use into their code. (Contributed by Donghee Na and Terry J. Reedy in bpo-42299 .)

Removed the PyModule_GetWarningsModule() function that was useless now due to the _warnings module was converted to a builtin module in 2.6. (Contributed by Hai Shi in bpo-42599 .)

Remove deprecated aliases to Collections Abstract Base Classes from the collections module. (Contributed by Victor Stinner in bpo-37324 .)

The loop parameter has been removed from most of asyncio ‘s high-level API following deprecation in Python 3.8. The motivation behind this change is multifold:

This simplifies the high-level API.

The functions in the high-level API have been implicitly getting the current thread’s running event loop since Python 3.7. There isn’t a need to pass the event loop to the API in most normal use cases.

Event loop passing is error-prone especially when dealing with loops running in different threads.

Note that the low-level API will still accept loop . See Changes in the Python API for examples of how to replace existing code.

(Contributed by Yurii Karabas, Andrew Svetlov, Yury Selivanov and Kyle Stanley in bpo-42392 .)

Porting to Python 3.10 ¶

This section lists previously described changes and other bugfixes that may require changes to your code.

Changes in the Python syntax ¶

Deprecation warning is now emitted when compiling previously valid syntax if the numeric literal is immediately followed by a keyword (like in 0in x ). In future releases it will be changed to syntax warning, and finally to a syntax error. To get rid of the warning and make the code compatible with future releases just add a space between the numeric literal and the following keyword. (Contributed by Serhiy Storchaka in bpo-43833 .)

Changes in the Python API ¶

The etype parameters of the format_exception() , format_exception_only() , and print_exception() functions in the traceback module have been renamed to exc . (Contributed by Zackery Spytz and Matthias Bussonnier in bpo-26389 .)

atexit : At Python exit, if a callback registered with atexit.register() fails, its exception is now logged. Previously, only some exceptions were logged, and the last exception was always silently ignored. (Contributed by Victor Stinner in bpo-42639 .)

collections.abc.Callable generic now flattens type parameters, similar to what typing.Callable currently does. This means that collections.abc.Callable[[int, str], str] will have __args__ of (int, str, str) ; previously this was ([int, str], str) . Code which accesses the arguments via typing.get_args() or __args__ need to account for this change. Furthermore, TypeError may be raised for invalid forms of parameterizing collections.abc.Callable which may have passed silently in Python 3.9. (Contributed by Ken Jin in bpo-42195 .)

socket.htons() and socket.ntohs() now raise OverflowError instead of DeprecationWarning if the given parameter will not fit in a 16-bit unsigned integer. (Contributed by Erlend E. Aasland in bpo-42393 .)

The loop parameter has been removed from most of asyncio ‘s high-level API following deprecation in Python 3.8.

A coroutine that currently looks like this:

Should be replaced with this:

If foo() was specifically designed not to run in the current thread’s running event loop (e.g. running in another thread’s event loop), consider using asyncio.run_coroutine_threadsafe() instead.

The types.FunctionType constructor now inherits the current builtins if the globals dictionary has no "__builtins__" key, rather than using {"None": None} as builtins: same behavior as eval() and exec() functions. Defining a function with def function(...): ... in Python is not affected, globals cannot be overridden with this syntax: it also inherits the current builtins. (Contributed by Victor Stinner in bpo-42990 .)

Changes in the C API ¶

The C API functions PyParser_SimpleParseStringFlags , PyParser_SimpleParseStringFlagsFilename , PyParser_SimpleParseFileFlags , PyNode_Compile and the type used by these functions, struct _node , were removed due to the switch to the new PEG parser.

Source should be now be compiled directly to a code object using, for example, Py_CompileString() . The resulting code object can then be evaluated using, for example, PyEval_EvalCode() .

Specifically:

A call to PyParser_SimpleParseStringFlags followed by PyNode_Compile can be replaced by calling Py_CompileString() .

There is no direct replacement for PyParser_SimpleParseFileFlags . To compile code from a FILE * argument, you will need to read the file in C and pass the resulting buffer to Py_CompileString() .

To compile a file given a char * filename, explicitly open the file, read it and compile the result. One way to do this is using the io module with PyImport_ImportModule() , PyObject_CallMethod() , PyBytes_AsString() and Py_CompileString() , as sketched below. (Declarations and error handling are omitted.)

For FrameObject objects, the f_lasti member now represents a wordcode offset instead of a simple offset into the bytecode string. This means that this number needs to be multiplied by 2 to be used with APIs that expect a byte offset instead (like PyCode_Addr2Line() for example). Notice as well that the f_lasti member of FrameObject objects is not considered stable: please use PyFrame_GetLineNumber() instead.

CPython bytecode changes ¶

The MAKE_FUNCTION instruction now accepts either a dict or a tuple of strings as the function’s annotations. (Contributed by Yurii Karabas and Inada Naoki in bpo-42202 .)

Build Changes ¶

PEP 644 : Python now requires OpenSSL 1.1.1 or newer. OpenSSL 1.0.2 is no longer supported. (Contributed by Christian Heimes in bpo-43669 .)

The C99 functions snprintf() and vsnprintf() are now required to build Python. (Contributed by Victor Stinner in bpo-36020 .)

sqlite3 requires SQLite 3.7.15 or higher. (Contributed by Sergey Fedoseev and Erlend E. Aasland in bpo-40744 and bpo-40810 .)

The atexit module must now always be built as a built-in module. (Contributed by Victor Stinner in bpo-42639 .)

Add --disable-test-modules option to the configure script: don’t build nor install test modules. (Contributed by Xavier de Gaye, Thomas Petazzoni and Peixing Xin in bpo-27640 .)

Add --with-wheel-pkg-dir=PATH option to the ./configure script. If specified, the ensurepip module looks for setuptools and pip wheel packages in this directory: if both are present, these wheel packages are used instead of ensurepip bundled wheel packages.

Some Linux distribution packaging policies recommend against bundling dependencies. For example, Fedora installs wheel packages in the /usr/share/python-wheels/ directory and don’t install the ensurepip._bundled package.

(Contributed by Victor Stinner in bpo-42856 .)

Add a new configure --without-static-libpython option to not build the libpythonMAJOR.MINOR.a static library and not install the python.o object file.

(Contributed by Victor Stinner in bpo-43103 .)

The configure script now uses the pkg-config utility, if available, to detect the location of Tcl/Tk headers and libraries. As before, those locations can be explicitly specified with the --with-tcltk-includes and --with-tcltk-libs configuration options. (Contributed by Manolis Stamatogiannakis in bpo-42603 .)

Add --with-openssl-rpath option to configure script. The option simplifies building Python with a custom OpenSSL installation, e.g. ./configure --with-openssl=/path/to/openssl --with-openssl-rpath=auto . (Contributed by Christian Heimes in bpo-43466 .)

C API Changes ¶

Pep 652: maintaining the stable abi ¶.

The Stable ABI (Application Binary Interface) for extension modules or embedding Python is now explicitly defined. C API Stability describes C API and ABI stability guarantees along with best practices for using the Stable ABI.

(Contributed by Petr Viktorin in PEP 652 and bpo-43795 .)

The result of PyNumber_Index() now always has exact type int . Previously, the result could have been an instance of a subclass of int . (Contributed by Serhiy Storchaka in bpo-40792 .)

Add a new orig_argv member to the PyConfig structure: the list of the original command line arguments passed to the Python executable. (Contributed by Victor Stinner in bpo-23427 .)

The PyDateTime_DATE_GET_TZINFO() and PyDateTime_TIME_GET_TZINFO() macros have been added for accessing the tzinfo attributes of datetime.datetime and datetime.time objects. (Contributed by Zackery Spytz in bpo-30155 .)

Add a PyCodec_Unregister() function to unregister a codec search function. (Contributed by Hai Shi in bpo-41842 .)

The PyIter_Send() function was added to allow sending value into iterator without raising StopIteration exception. (Contributed by Vladimir Matveev in bpo-41756 .)

Add PyUnicode_AsUTF8AndSize() to the limited C API. (Contributed by Alex Gaynor in bpo-41784 .)

Add PyModule_AddObjectRef() function: similar to PyModule_AddObject() but don’t steal a reference to the value on success. (Contributed by Victor Stinner in bpo-1635741 .)

Add Py_NewRef() and Py_XNewRef() functions to increment the reference count of an object and return the object. (Contributed by Victor Stinner in bpo-42262 .)

The PyType_FromSpecWithBases() and PyType_FromModuleAndSpec() functions now accept a single class as the bases argument. (Contributed by Serhiy Storchaka in bpo-42423 .)

The PyType_FromModuleAndSpec() function now accepts NULL tp_doc slot. (Contributed by Hai Shi in bpo-41832 .)

The PyType_GetSlot() function can accept static types . (Contributed by Hai Shi and Petr Viktorin in bpo-41073 .)

Add a new PySet_CheckExact() function to the C-API to check if an object is an instance of set but not an instance of a subtype. (Contributed by Pablo Galindo in bpo-43277 .)

Add PyErr_SetInterruptEx() which allows passing a signal number to simulate. (Contributed by Antoine Pitrou in bpo-43356 .)

The limited C API is now supported if Python is built in debug mode (if the Py_DEBUG macro is defined). In the limited C API, the Py_INCREF() and Py_DECREF() functions are now implemented as opaque function calls, rather than accessing directly the PyObject.ob_refcnt member, if Python is built in debug mode and the Py_LIMITED_API macro targets Python 3.10 or newer. It became possible to support the limited C API in debug mode because the PyObject structure is the same in release and debug mode since Python 3.8 (see bpo-36465 ).

The limited C API is still not supported in the --with-trace-refs special build ( Py_TRACE_REFS macro). (Contributed by Victor Stinner in bpo-43688 .)

Add the Py_Is(x, y) function to test if the x object is the y object, the same as x is y in Python. Add also the Py_IsNone() , Py_IsTrue() , Py_IsFalse() functions to test if an object is, respectively, the None singleton, the True singleton or the False singleton. (Contributed by Victor Stinner in bpo-43753 .)

Add new functions to control the garbage collector from C code: PyGC_Enable() , PyGC_Disable() , PyGC_IsEnabled() . These functions allow to activate, deactivate and query the state of the garbage collector from C code without having to import the gc module.

Add a new Py_TPFLAGS_DISALLOW_INSTANTIATION type flag to disallow creating type instances. (Contributed by Victor Stinner in bpo-43916 .)

Add a new Py_TPFLAGS_IMMUTABLETYPE type flag for creating immutable type objects: type attributes cannot be set nor deleted. (Contributed by Victor Stinner and Erlend E. Aasland in bpo-43908 .)

The PY_SSIZE_T_CLEAN macro must now be defined to use PyArg_ParseTuple() and Py_BuildValue() formats which use # : es# , et# , s# , u# , y# , z# , U# and Z# . See Parsing arguments and building values and PEP 353 . (Contributed by Victor Stinner in bpo-40943 .)

Since Py_REFCNT() is changed to the inline static function, Py_REFCNT(obj) = new_refcnt must be replaced with Py_SET_REFCNT(obj, new_refcnt) : see Py_SET_REFCNT() (available since Python 3.9). For backward compatibility, this macro can be used:

(Contributed by Victor Stinner in bpo-39573 .)

Calling PyDict_GetItem() without GIL held had been allowed for historical reason. It is no longer allowed. (Contributed by Victor Stinner in bpo-40839 .)

PyUnicode_FromUnicode(NULL, size) and PyUnicode_FromStringAndSize(NULL, size) raise DeprecationWarning now. Use PyUnicode_New() to allocate Unicode object without initial data. (Contributed by Inada Naoki in bpo-36346 .)

The private _PyUnicode_Name_CAPI structure of the PyCapsule API unicodedata.ucnhash_CAPI has been moved to the internal C API. (Contributed by Victor Stinner in bpo-42157 .)

Py_GetPath() , Py_GetPrefix() , Py_GetExecPrefix() , Py_GetProgramFullPath() , Py_GetPythonHome() and Py_GetProgramName() functions now return NULL if called before Py_Initialize() (before Python is initialized). Use the new Python Initialization Configuration API to get the Python Path Configuration . (Contributed by Victor Stinner in bpo-42260 .)

PyList_SET_ITEM() , PyTuple_SET_ITEM() and PyCell_SET() macros can no longer be used as l-value or r-value. For example, x = PyList_SET_ITEM(a, b, c) and PyList_SET_ITEM(a, b, c) = x now fail with a compiler error. It prevents bugs like if (PyList_SET_ITEM (a, b, c) < 0) ... test. (Contributed by Zackery Spytz and Victor Stinner in bpo-30459 .)

The non-limited API files odictobject.h , parser_interface.h , picklebufobject.h , pyarena.h , pyctype.h , pydebug.h , pyfpe.h , and pytime.h have been moved to the Include/cpython directory. These files must not be included directly, as they are already included in Python.h ; see Include Files . If they have been included directly, consider including Python.h instead. (Contributed by Nicholas Sim in bpo-35134 .)

Use the Py_TPFLAGS_IMMUTABLETYPE type flag to create immutable type objects. Do not rely on Py_TPFLAGS_HEAPTYPE to decide if a type object is mutable or not; check if Py_TPFLAGS_IMMUTABLETYPE is set instead. (Contributed by Victor Stinner and Erlend E. Aasland in bpo-43908 .)

The undocumented function Py_FrozenMain has been removed from the limited API. The function is mainly useful for custom builds of Python. (Contributed by Petr Viktorin in bpo-26241 .)

The PyUnicode_InternImmortal() function is now deprecated and will be removed in Python 3.12: use PyUnicode_InternInPlace() instead. (Contributed by Victor Stinner in bpo-41692 .)

Removed Py_UNICODE_str* functions manipulating Py_UNICODE* strings. (Contributed by Inada Naoki in bpo-41123 .)

Py_UNICODE_strlen : use PyUnicode_GetLength() or PyUnicode_GET_LENGTH

Py_UNICODE_strcat : use PyUnicode_CopyCharacters() or PyUnicode_FromFormat()

Py_UNICODE_strcpy , Py_UNICODE_strncpy : use PyUnicode_CopyCharacters() or PyUnicode_Substring()

Py_UNICODE_strcmp : use PyUnicode_Compare()

Py_UNICODE_strncmp : use PyUnicode_Tailmatch()

Py_UNICODE_strchr , Py_UNICODE_strrchr : use PyUnicode_FindChar()

Removed PyUnicode_GetMax() . Please migrate to new ( PEP 393 ) APIs. (Contributed by Inada Naoki in bpo-41103 .)

Removed PyLong_FromUnicode() . Please migrate to PyLong_FromUnicodeObject() . (Contributed by Inada Naoki in bpo-41103 .)

Removed PyUnicode_AsUnicodeCopy() . Please use PyUnicode_AsUCS4Copy() or PyUnicode_AsWideCharString() (Contributed by Inada Naoki in bpo-41103 .)

Removed _Py_CheckRecursionLimit variable: it has been replaced by ceval.recursion_limit of the PyInterpreterState structure. (Contributed by Victor Stinner in bpo-41834 .)

Removed undocumented macros Py_ALLOW_RECURSION and Py_END_ALLOW_RECURSION and the recursion_critical field of the PyInterpreterState structure. (Contributed by Serhiy Storchaka in bpo-41936 .)

Removed the undocumented PyOS_InitInterrupts() function. Initializing Python already implicitly installs signal handlers: see PyConfig.install_signal_handlers . (Contributed by Victor Stinner in bpo-41713 .)

Remove the PyAST_Validate() function. It is no longer possible to build a AST object ( mod_ty type) with the public C API. The function was already excluded from the limited C API ( PEP 384 ). (Contributed by Victor Stinner in bpo-43244 .)

Remove the symtable.h header file and the undocumented functions:

PyST_GetScope()

PySymtable_Build()

PySymtable_BuildObject()

PySymtable_Free()

Py_SymtableString()

Py_SymtableStringObject()

The Py_SymtableString() function was part the stable ABI by mistake but it could not be used, because the symtable.h header file was excluded from the limited C API.

Use Python symtable module instead. (Contributed by Victor Stinner in bpo-43244 .)

Remove PyOS_ReadlineFunctionPointer() from the limited C API headers and from python3.dll , the library that provides the stable ABI on Windows. Since the function takes a FILE* argument, its ABI stability cannot be guaranteed. (Contributed by Petr Viktorin in bpo-43868 .)

Remove ast.h , asdl.h , and Python-ast.h header files. These functions were undocumented and excluded from the limited C API. Most names defined by these header files were not prefixed by Py and so could create names conflicts. For example, Python-ast.h defined a Yield macro which was conflict with the Yield name used by the Windows <winbase.h> header. Use the Python ast module instead. (Contributed by Victor Stinner in bpo-43244 .)

Remove the compiler and parser functions using struct _mod type, because the public AST C API was removed:

PyAST_Compile()

PyAST_CompileEx()

PyAST_CompileObject()

PyFuture_FromAST()

PyFuture_FromASTObject()

PyParser_ASTFromFile()

PyParser_ASTFromFileObject()

PyParser_ASTFromFilename()

PyParser_ASTFromString()

PyParser_ASTFromStringObject()

These functions were undocumented and excluded from the limited C API. (Contributed by Victor Stinner in bpo-43244 .)

Remove the pyarena.h header file with functions:

PyArena_New()

PyArena_Free()

PyArena_Malloc()

PyArena_AddPyObject()

These functions were undocumented, excluded from the limited C API, and were only used internally by the compiler. (Contributed by Victor Stinner in bpo-43244 .)

The PyThreadState.use_tracing member has been removed to optimize Python. (Contributed by Mark Shannon in bpo-43760 .)

Notable security feature in 3.10.7 ¶

Converting between int and str in bases other than 2 (binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now raises a ValueError if the number of digits in string form is above a limit to avoid potential denial of service attacks due to the algorithmic complexity. This is a mitigation for CVE 2020-10735 . This limit can be configured or disabled by environment variable, command line flag, or sys APIs. See the integer string conversion length limitation documentation. The default limit is 4300 digits in string form.

Notable security feature in 3.10.8 ¶

The deprecated mailcap module now refuses to inject unsafe text (filenames, MIME types, parameters) into shell commands. Instead of using such text, it will warn and act as if a match was not found (or for test commands, as if the test failed). (Contributed by Petr Viktorin in gh-98966 .)

Notable changes in 3.10.12 ¶

The extraction methods in tarfile , and shutil.unpack_archive() , have a new a filter argument that allows limiting tar features than may be surprising or dangerous, such as creating files outside the destination directory. See Extraction filters for details. In Python 3.12, use without the filter argument will show a DeprecationWarning . In Python 3.14, the default will switch to 'data' . (Contributed by Petr Viktorin in PEP 706 .)

Table of Contents

• Summary – Release highlights
• Parenthesized context managers
• SyntaxErrors
• IndentationErrors
• AttributeErrors
• PEP 626: Precise line numbers for debugging and other tools
• Syntax and operations
• Declarative approach
• Behavior without the wildcard
• Patterns with a literal and variable
• Patterns with positional parameters
• Nested patterns
• Complex patterns and the wildcard
• Other Key Features
• Optional EncodingWarning and encoding="locale" option
• PEP 604: New Type Union Operator
• PEP 612: Parameter Specification Variables
• PEP 613: TypeAlias
• PEP 647: User-Defined Type Guards
• Other Language Changes
• New Modules
• asynchat, asyncore, smtpd
• collections.abc
• Keyword-only fields
• faulthandler
• IDLE and idlelib
• importlib.metadata
• urllib.parse
• Optimizations
• Changes in the Python syntax
• Changes in the Python API
• Changes in the C API
• CPython bytecode changes
• Build Changes
• PEP 652: Maintaining the Stable ABI
• New Features
• Porting to Python 3.10
• Notable security feature in 3.10.7
• Notable security feature in 3.10.8

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