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Python 类型提示(Type Hints)

动态类型语言有一个优点,同时也是缺点:不好做静态类型检查,IDE 或者其他开发工具很难根据代码去准确判断一个变量的类型。
Python 3.0 开始引入并逐渐完善类型注解(Type Annotation)则给 Python 静态类型检查提供了可能性。
PS: Python 运行时会忽略类型注解,不会给任何提示或警告。
PS: 之前的一些工具可以通过注释来做类型检查 (Type Comment),起到相同的作用。

PEP

SF 3107 [2006-12-02] (3.0 ) Function Annotations  开始引入函数注解
SF 3141 [2007-04-23] (    ) A Type Hierarchy for Numbers
SF  424 [2012-07-14] (3.4 ) A method for exposing a length hint
SF  451 [2013-08-08] (3.4 ) A ModuleSpec Type for the Import System
SP  484 [2014-09-29] (3.5 ) Type Hints            类型提示
IF  483 [2014-12-19] (    ) The Theory of Type Hints
IF  482 [2015-01-08] (    ) Literature Overview for Type Hints
SF  526 [2016-08-09] (3.6 ) Syntax for Variable Annotations
SA  544 [2017-03-05] (3.8 ) Protocols: Structural subtyping (static duck typing)
SA  560 [2017-09-03] (3.7 ) Core support for typing module and generic types
SA  563 [2017-09-08] (3.7 ) Postponed Evaluation of Annotations
SA  561 [2017-09-09] (3.7 ) Distributing and Packaging Type Information
SA  585 [2019-03-03] (3.9 ) Type Hinting Generics In Standard Collections
SA  586 [2019-03-14] (3.8 ) Literal Types
SA  591 [2019-03-15] (3.8 ) Adding a final qualifier to typing
SA  589 [2019-03-20] (3.8 ) TypedDict: Type Hints for Dictionaries with a Fixed Set of Keys
SA  593 [2019-04-26] (3.9 ) Flexible function and variable annotations
SA  604 [2019-08-28] (3.10) Allow writing union types as ``X | Y``
SA  613 [2020-01-21] (    ) Explicit Type Aliases     引入类型别名
SA  647 [2020-10-07] (3.10) User-Defined Type Guards  引入 TypeGuard 类型,缩小类型检查时的范围
S   649 [2021-01-11] (    ) Deferred Evaluation Of Annotations Using Descriptors
S   655 [2021-01-30] (3.10) Marking individual TypedDict items as required or potentially-missing

基础用法

如果担心类型检查会,可以使用 @no_type_check 装饰器。

def greeting(name: str) -> str:
    return 'Hello ' + name

Vector = list[float]

def scale(scalar: float, vector: Vector) -> Vector:
    return [scalar * num for num in vector]

Union

from typing import NoReturn

Address = tuple[str, int]

def connect(Union[Address, str]) -> NoReturn:
    pass

Optional[T]Union[T, None] 的简写。

def get_argument(name:str, default:Optional[str]=None) -> Union[str, None]:
    pass

其他常用类型

  • Any
  • Callable
  • ClassVar
  • NewType

stub 文件

https://github.com/python/typeshed
Collection of library stubs for Python, with static types

类型检查工具

IDE,比如 PyCharm,可以配置类型检查。
VSCode 或者 Atom 之类的编辑器也可以通过插件支持类型检查。

  1. mypy
  2. pyright
  3. pytype
  4. pyre

参考:
- https://github.com/topics/typechecker?l=python&stars:%3E1000
- https://github.com/search?q=type+python+stars%3A%3E3000&s=stars&o=desc

mypy

参考资料与拓展阅读