How can I specify the function type in my type hints?

My specific use case for wanting this functionality was to enable rich code completion in PyCharm. Using Callable didn't cause PyCharm to suggest that the object had a .__code__ attribute, which is what I wanted, in this case.

I stumbled across the types module and..

from types import FunctionType

allowed me to annotate an object with FunctionType and, voilà, PyCharm now suggests my object has a .__code__ attribute.

The OP wasn't clear on why this type hint was useful to them. Callable certainly works for anything that implements .__call__() but for further interface clarification, I submit the types module.

Bummer that Python needed two very similar modules.

As @jonrsharpe noted in a comment, this can be done with typing.Callable:

from typing import Callable

def my_function(func: Callable):

Note: Callable on its own is equivalent to Callable[..., Any]. Such a Callable takes any number and type of arguments (...) and returns a value of any type (Any). If this is too unconstrained, one may also specify the types of the input argument list and return type.

For example, given:

def sum(a: int, b: int) -> int: return a+b

The corresponding annotation is:

Callable[[int, int], int]

That is, the parameters are sub-scripted in the outer subscription with the return type as the second element in the outer subscription. In general:

Callable[[ParamType1, ParamType2, .., ParamTypeN], ReturnType]

Another interesting point to note is that you can use the built in function type() to get the type of a built in function and use that. So you could have

def f(my_function: type(abs)) -> int:
    return my_function(100)

Or something of that form