Python type hints and `*args`

Question

Assume I have a function like this:

def foo(*args):
    for x in args:
        print(x)

and let's say I want to say that all the elements of args are int; what is the right way to express it as of PEP 0484? Should I do something like

from typing import Tuple


def foo(*args: Tuple[int, ...]) -> None:
    for x in args:
        print(x)

or something like

def foo(*args: int) -> None:
    for x in args:
        print(x)

or something else entirely?

In particular, I'm trying to use type hints effectively in PyCharm, and none of the solutions I've thought of seems to help PyCharm understand that x should be an int.

Answer 1

According to PEP-484:

Arbitrary argument lists can as well be type annotated, so that the definition:

def foo(*args: str, **kwds: int): ...

is acceptable and it means that, e.g., all of the following represent function calls with valid types of arguments:

foo('a', 'b', 'c')
foo(x=1, y=2)
foo('', z=0)

In the body of function foo, the type of variable args is deduced as Tuple[str, ...] and the type of variable kwds is Dict[str, int].

The correct way to annotate the foo function from your example is:

def foo(*args: int) -> None:
    for x in args:
        print(x)

In Python 2:

def foo(*args):
    # type: (*int) -> None
    for x in args:
        print(x)