How to write a test that checks if was added type annotation in function?

I have a function.

def func(num: int, item: str) -> list:
   pass

And I want to add a test that checks that function and parameters have a type annotation. It is needed by other developers don’t change input and output types.

Any idea how to do that? I want to use pytest, maybe mocks?

Answer

You can use the get_type_hints function from typing:

import typing
from typing import Callable


def func(num: int, item: str) -> list:
    pass


def func_bad(num, item):
    pass


def test_has_annotation(f: Callable) -> bool:
    hints = typing.get_type_hints(f)
    print(hints)  # to check what this returns
    return bool(hints)


print(test_has_annotation(func))
print(test_has_annotation(func_bad))

Result:

{'num': <class 'int'>, 'item': <class 'str'>, 'return': <class 'list'>}
True
{}
False