Python3.10 新特性

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Python3.10 新特性

简介

Python3.10 发布于2021年10月14日，这儿总结一下改版本引入的一些新功能

官方新特性链接 Python3.10 新特性

安装

此处主要介绍在Ubuntu下安装 Python3.10

  1. 添加deadsnakes源
    • sudo add-apt-repository ppa:deadsnakes/ppa
    • sudo apt-get update
  2. 安装 Python3.10
    • sudo apt install python3.10-full
  3. 安装 Python3.10 的pip
    • python3.10 -m ensurepip --upgrade

结构模式匹配（match case）

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# 通用语法

match subject:
    case <pattern_1>:
        <action_1>
    case <pattern_2>:
        <action_2>
    case <pattern_3>:
        <action_3>
    case _:
        <action_wildcard>
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def http_error(status):
    match status:
        case 400:
            return "Bad request"
        case 404:
            return "Not found"
        case 418:
            return "I'm a teapot"
        case 455 | 456:
            return "This is a custom error"
        case _:
            return "Something's wrong with the Internet"

print(http_error(418))
print(http_error(455))
print(http_error(456))
print(http_error(499))

# I'm a teapot
# This is a custom error
# This is a custom error
# Something's wrong with the Internet

带有字面值和变量的模式

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# point is an (x, y) tuple
match point:
    case (0, 0):
        print("Origin")
    case (0, y):
        print(f"Y={y}")
    case (x, 0):
        print(f"X={x}")
    case (x, y):
        print(f"X={x}, Y={y}")
    case _:
        raise ValueError("Not a point")

模式和类

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class Point:
    x: int
    y: int

def location(point):
    match point:
        case Point(x=0, y=0):
            print("Origin is the point's location.")
        case Point(x=0, y=y):
            print(f"Y={y} and the point is on the y-axis.")
        case Point(x=x, y=0):
            print(f"X={x} and the point is on the x-axis.")
        case Point():
            print("The point is located somewhere else on the plane.")
        case _:
            print("Not a point")

约束项

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match point:
    case Point(x, y) if x == y:
        print(f"The point is located on the diagonal Y=X at {x}.")
    case Point(x, y):
        print(f"Point is not on the diagonal.")

复杂模式和通配符

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match test_variable:
    case ('warning', code, 40):
        print("A warning has been received.")
    case ('error', code, _):
        print(f"An error {code} occurred.")

更好的错误信息

语法错误（SynaxErrors）

字典未关闭

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test_dict = {1: 1, 2: 2, 3: 3

# Python3.9
"""
  File "/home/stolen/test.py", line 2
   
    ^
SyntaxError: unexpected EOF while parsing
"""

# Python3.10
"""
  File "/home/stolen/test.py", line 1
    test_dict = {1: 1, 2: 2, 3: 3
                ^
SyntaxError: '{' was never closed
"""

冒号缺失

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if 1 > 2
    print('abc')

# Python3.9
"""
  File "/home/stolen/test.py", line 1
    if 1 > 2
            ^
SyntaxError: invalid syntax
"""

# Python3.10
"""
  File "/home/stolen/test.py", line 1
    if 1 > 2
            ^
SyntaxError: expected ':'
"""

判断等于错误

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if bool(3.14) = True:
    print('true')

# Python3.9
"""
  File "/home/stolen/test.py", line 1
    if bool(3.14) = True:
                  ^
SyntaxError: invalid syntax
"""

# Python3.10
"""
  File "/home/stolen/test.py", line 1
    if bool(3.14) = True:
       ^^^^^^^^^^
SyntaxError: cannot assign to function call here. Maybe you meant '==' instead of '='?
"""

缩进错误（IndentationErrors）

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if bool(3.14) == True:
print('true')

# Python3.9
"""
  File "/home/project/demo.py", line 2
    print('true')
    ^
IndentationError: expected an indented block
"""

# Python3.10
"""
  File "/home/project/demo.py", line 2
    print('true')
    ^
IndentationError: expected an indented block after 'if' statement on line 1
"""

属性错误（AttributeErrors）

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a = 'abc'
a.isnumerics()

# Python3.9
"""
Traceback (most recent call last):
  File "/home/project/demo.py", line 2, in <module>
    a.isnumerics()
AttributeError: 'str' object has no attribute 'isnumerics'
"""

# Python3.10
"""
Traceback (most recent call last):
  File "/home/project/demo.py", line 2, in <module>
    a.isnumerics()
AttributeError: 'str' object has no attribute 'isnumerics'. Did you mean: 'isnumeric'?
"""

命名错误（NameErrors）

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hello = 'hello, world!'
print(hallo)

# Python3.9
"""
Traceback (most recent call last):
  File "/home/project/demo.py", line 2, in <module>
    print(hallo)
NameError: name 'hallo' is not defined
"""

# Python3.10
"""
Traceback (most recent call last):
  File "/home/project/demo.py", line 2, in <module>
    print(hallo)
NameError: name 'hallo' is not defined. Did you mean: 'hello'?
"""

类型提示相关的新功能

从 Python3.5 开始正式引入 typing 模块，从 Python3.6 开始已经获得全面的类型声明的支持，一下将介绍 Python3.10 中的变化

Union 可以用 | 简写

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# Python3.9
from typing import Union
def square(number: Union[int, float]) -> Union[int, float]:
    return number ** 2

# Python3.10
def square(number: int | float) -> int | float:
    return number ** 2

这种语法也可以用在 isinstance 中 isinstance(item, int | str)

类型别名

现在可以对类型别名变量做TypeHint

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# Python3.9
MyType = str
def foo(something: MyType) -> MyType:
    return something

# Python3.10
from typing import TypeAlias
MyType: TypeAlias = str
def foo(something: MyType) -> MyType:
    return something

带括号的上下文管理器

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with (CtxManager() as example):
    ...

with (
    CtxManager1(),
    CtxManager2()
):
    ...

with (CtxManager1() as example,
      CtxManager2()):
    ...

with (CtxManager1(),
      CtxManager2() as example):
    ...

with (
    CtxManager1() as example1,
    CtxManager2() as example2
):
    ...

zip的长度检查

默认情况下 zip 在最短的迭代次数用尽时停止，现在加入了一个 strict=False 参数，默认情况不检查长度，如果 strict=True 时，如果可迭代项长度不相等，则会引发 ValueError

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list(zip(range(3), ['a', 'b', 'c', 'd'], strict=True))
# [(0, 'a'), (1, 'b'), (2, 'c')]

list(zip(range(3), ['a', 'b', 'c', 'd'], strict=True))
# ValueError: zip() argument 2 is longer than argument 1

字典视图映射

字典的三个方法 dict.keys()、dict.values() 和 dict.items() 会返回不同的视图，现在都增加了 mapping 属性，可以返回原始字典。

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data={'python':2021,'java':2020}
k=data.keys()
print(k)
print(k.mapping)

# dict_keys(['python', 'java'])
# {'python': 2021, 'java': 2020}

为整数添加 popcount 计算方法

汉明重量是一串符号中非零符号的个数,是以理查德·卫斯里·汉明的名字命名的，它在包括信息论、编码理论、密码学等多个领域都有应用。

在密码学以及其它应用中经常需要计算数据位中 1 的个数，针对如何高效地实现人们已经广泛地进行了研究。

Python3.10 为整数类型增加了一个新方法 int.bit_count() 可以返回给定整数的二进制位中 1 的个数。

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a = 11
print(bin(a))    #a的二进制表示
print(a.bit_count())

# 0b1011
# 3