How to inspect return type of Callable

Question

Let’s say I have something like the following:

import inspect
from collections.abc import Callable  # Using Python 3.10+
from typing import get_type_hints

def foo(arg: Callable[..., int]) -> None:
    pass

type_hints = get_type_hints(foo)["arg"]
annotation = inspect.signature(foo).parameters["arg"].annotation
# How can one get the return type `int` from either of these?

I can figure out how to get to the Callable type hint. From there, how can one inspect the return type of the Callable?

Asked By: Intrastellar Explorer

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Source

Answer 1

annotation.__args__

or

type_hints.__args__

(Ellipsis, <class 'int'>)

Answered By: Tom McLean

Answer 2

To avoid access to dunder attributes, which in general is unsafe and can break between version releases, you should use a method provided by typing module:

type_hint = get_type_hints(foo)["arg"]
arg_types, return_type = get_args(type_hint)

This works for any Callable. arg_types is Ellipsis (...) or a list of args (also may be a typing.ParamSpec or typing.Concatenate, if you use them), return_type is whatever occupies 2nd place.

Answered By: SUTerliakov

How to inspect return type of Callable

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