解压缩Python的类型注释 [英] Unpacking Python's Type Annotations

问题描述

我正在尝试通过使用inspect模块中的signature()函数，根据我在某些Python函数中提供的类型注释来生成一些JavaScript.

I'm trying to generate some JavaScript based on the type annotations I have provided in on some Python functions by using the signature() function in the inspect module.

当类型是一个简单的内置类时，这部分按我的预期工作:

This part works as I expect when the type is a simple builtin class:

import inspect

def my_function() -> dict:
    pass

signature = inspect.signature(my_function)
signature.return_annotation is dict  # True

尽管我不确定如何解开和检查更复杂的注释，例如:

Though I'm not sure how to unwrap and inspect more complex annotations e.g:

from typing import List
import inspect

def my_function() -> List[int]:
    pass

signature = inspect.signature(my_function)
signature.return_annotation is List[int]  # False

转发引用自定义类也遇到类似的问题:

Again similar problem with forward referencing a custom class:

def my_function() -> List['User']:
    pass
...
signature.return_annotation  # typing.List[_ForwardRef('User')]

我想要得到的是这样的东西-因此我可以在生成JavaScript时适当地分支:

What I'm looking to get out is something like this - so I can branch appropriately while generating the JavaScript:

type = signature.return_annotation... # list
member_type = signature.return_annotation... # int / 'User'

谢谢.

推荐答案

Python 3.8为此提供了typing.get_origin()和typing.get_args()！

Python 3.8 provides typing.get_origin() and typing.get_args() for this!

assert get_origin(Dict[str, int]) is dict
assert get_args(Dict[int, str]) == (int, str)

assert get_origin(Union[int, str]) is Union
assert get_args(Union[int, str]) == (int, str)

请参见 https://docs.python.org/3/library/typing.html#typing.get_origin

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