How can I specify the function type in my type hin

问题:

I want to use type hints in my current Python 3.5 project. My function should receive a function as parameter.

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

import typing

def my_function(name:typing.AnyStr, func: typing.Function) -> None:
    # However, typing.Function does not exist.
    # How can I specify the type function for the parameter `func`?

    # do some processing
    pass

I checked PEP 483, but could not find a function type hint there.

回答1:

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

from typing import AnyStr, Callable

def my_function(name: AnyStr, func: Callable) -> None:

Issue is, Callable on it's own is translated to Callable[..., Any] which means:

A callable takes any number of/type of arguments and returns a value of any type. In most cases, this isn't what you want since you'll allow pretty much any function to be passed. You want the function parameters and return types to be hinted too.

That's why many types in typing have been overloaded to support sub-scripting which denotes these extra types. So if, for example, you had a function sum that takes two ints and returns an int:

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

Your annotation for it would be:

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]

回答2:

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