Python type hinting for List with possible values

Question

I have a function:

def foo(a, b):
  return [a, b]

I want to add type hinting for return value, as you can see my function can return [srt, int] or [str, str] or [int, int] etc. for example.

I tried:

def foo(a, b) -> List[str, int]:
  return [a, b]

but it not working.

How can I specify possible value in list that my function can return?

Riccardo Bucco · Accepted Answer · 2021-05-25 15:09:39Z

3

You can use Union. Specifically, Union[X, Y] means either X or Y.

from typing import List, Union

def foo(a, b) -> List[Union[str, int]]:
    return [a, b]

If your function can return a list containing any element, then use Any (special type indicating an unconstrained type):

from typing import Any, List

def foo(a, b) -> List[Any]:
    return [a, b]

answered May 25, 2021 at 14:40

Riccardo Bucco

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