如何访问typing.Generic 的类型参数?

问题描述

typing 模块提供了一个基类通用类型提示:typing.Generic 类.

Generic 的子类接受方括号中的类型参数，例如:

list_of_ints = typing.List[int]str_to_bool_dict = typing.Dict[str, bool]

我的问题是，如何访问这些类型参数?

也就是说，给定 str_to_bool_dict 作为输入，我怎样才能得到 str 和 bool 作为输出?

基本上我正在寻找这样的功能

>>>魔术函数(str_to_bool_dict)(<class 'str'>, <class 'bool'>)

解决方案

Python >= 3.8

从 Python3.8 开始，有 typing.get_args:

print( get_args( List[int] ) ) # (,)

PEP-560 还提供了 __orig_bases__[n]，它允许我们使用 n 个泛型基的参数:

 from 打字 import TypeVar, Generic, get_argsT = TypeVar(T")类基础(通用[T]):经过派生类( Base[int] ):经过打印(get_args(Derived.__orig_bases__[0]))#(<class 'int'>,)

---

Python >= 3.6

从 Python 3.6 开始.有一个公共 __args__ 和 (__parameters__) 字段.例如:

print( typing.List[int].__args__ )

这包含泛型参数(即 int)，而 __parameters__ 包含泛型本身(即 ~T).

---

Python <3.6

使用typing_inspect.getargs

---

一些注意事项

typing 遵循 PEP8.PEP8 和 typing 均由 Guido van Rossum 合着.双前导和尾随下划线定义为:存在于用户控制的命名空间"中的魔法"对象或属性.

dunders 也有内嵌注释；来自打字的官方存储库，我们可以看到:

• "__args__ 是用于下标的所有参数的元组，例如，Dict[T, int].__args__ == (T, int)".

然而，作者还注意到:

• "打字模块具有临时状态，因此它没有被高标准的向后兼容性所覆盖(尽管我们尽可能地保留它)，这对于(尚未记录的)dunder 来说尤其如此__union_params__ 等属性.如果您想在运行时上下文中使用类型，那么您可能对 typing_inspect 项目感兴趣(其中的一部分可能会在稍后输入)."

一般来说，无论您使用 typing 做什么，都需要暂时保持最新状态.如果您需要向前兼容的更改，我建议您编写自己的注释类.

The typing module provides a base class for generic type hints: The typing.Generic class.

Subclasses of Generic accept type arguments in square brackets, for example:

list_of_ints = typing.List[int]
str_to_bool_dict = typing.Dict[str, bool]

---

My question is, how can I access these type arguments?

That is, given str_to_bool_dict as input, how can I get str and bool as output?

Basically I'm looking for a function such that

>>> magic_function(str_to_bool_dict)
(<class 'str'>, <class 'bool'>)

解决方案

Python >= 3.8

As of Python3.8 there is typing.get_args:

print( get_args( List[int] ) ) # (<class 'int'>,)

PEP-560 also provides __orig_bases__[n], which allows us the arguments of the nth generic base:

from typing import TypeVar, Generic, get_args

T = TypeVar( "T" )

class Base( Generic[T] ):
    pass

class Derived( Base[int] ):
    pass

print( get_args( Derived.__orig_bases__[0] ) ) # (<class 'int'>,)

---

Python >= 3.6

As of Python 3.6. there is a public __args__ and (__parameters__) field.For instance:

print( typing.List[int].__args__ )

This contains the generic parameters (i.e. int), whilst __parameters__ contains the generic itself (i.e. ~T).

---

Python < 3.6

Use typing_inspect.getargs

---

Some considerations

typing follows PEP8. Both PEP8 and typing are coauthored by Guido van Rossum. A double leading and trailing underscore is defined in as: ""magic" objects or attributes that live in user-controlled namespaces".

The dunders are also commented in-line; from the official repository for typing wecan see:

• "__args__ is a tuple of all arguments used in subscripting, e.g., Dict[T, int].__args__ == (T, int)".

However, the authors also note:

• "The typing module has provisional status, so it is not covered by the high standards of backward compatibility (although we try to keep it as much as possible), this is especially true for (yet undocumented) dunder attributes like __union_params__. If you want to work with typing types in runtime context, then you may be interested in the typing_inspect project (part of which may end up in typing later)."

I general, whatever you do with typing will need to be kept up-to-date for the time being. If you need forward compatible changes, I'd recommend writing your own annotation classes.

这篇关于如何访问typing.Generic 的类型参数?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！