What's new in Python 3.10

Python 3.10 was released on October 4 2021. Today we are going to discuss the features of Python which in my opinion are the top five.

Structural Pattern Matching

Structural pattern matching is one of the most interesting features of Python 3.10. This is equivalent to switch case in other programming languages. The syntax for the same is as follows:

match subject:
    case <pattern 1>:
        <code block 1>
    case <pattern 2>:
        <code block 2>
    case <pattern 3>:
        <code block 3>
    case _:
        <default code block>

def print_day(day):
    match day:
        case 0:
            print("monday")
        case 1:
            print("tuesday")
        case 2:
            print("wednesday")
        case 3:
            print("thursday")
        case 4:
            print("friday")
        case 5:
            print("saturday")
        case 6:
            print("sunday")
        case _:
            print("not a valid day")

for i in range(8):
    print_day(i)

Output will be :

monday
tuesday
wednesday
thursday
friday
saturday
sunday
not a valid day

Parenthesized context managers

In Python 3.10, we can chain multiple context managers in a Parenthesis syntax for the same as follows

with (
    contextmanager1(),
    contextmanager2()):
    <Block>

with(open('file1.txt') as f1, open('file2.txt') as f2):
    print(f1.readlines())
    print(f2.readlines())

Improved error message

The error message in the new version is more detailed than the previous one. Consider the below example. Now the exact line number is also pointed out in the error message.

def function():
print("hello")

The previous message was

  File "inde_error.py", line 2
    print("hello")
    ^
IndentationError: expected an indented block

Now

  File "/home/afsal/Desktop/experiments/python310/inde_error.py", line 2
    print("hello")
    ^
IndentationError: expected an indented block after function definition on line 1

The new argument to the zip function

There is a new added argument to zip function. If this is set to true, then both the arguments must have the same length. Otherwise it will throw an error message.

Without argument

a = [1, 2, 3]
b = ["one", "two"]
print(list(zip(a, b)))

Output

[(1, 'one'), (2, 'two')]

With argument

a = [1, 2, 3]
b = ["one", "two"]
print(list(zip(a, b, strict=True)))

Output

Traceback (most recent call last):
  File "/home/afsal/Desktop/experiments/python310/zip_new.py", line 3, in <module>
    print(list(zip(a, b, strict=True)))
ValueError: zip() argument 2 is shorter than argument 1

New Type Union operator

They have added a new type of union operator. This can be done using the | operator. Previously we were using union from typing module

from typing import Union

def convert_to_negative(number: Union[int, float]) -> Union[int, float]:
    return -number

def convert_to_negative(number: int | str) -> int | str:
    return -number

isinstance(1, int | str)

There are no new modules. But a lot of improvements have been made. 

For more details, you may refer to the official documentation.

https://docs.python.org/3/whatsnew/3.10.html