CODEWITHSUNDEEP
pythonpycharmpython-typing
gcali
gcali

Reputation: 1248

Python type hints and `*args`

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.

Upvotes: 18

Views: 8555

Answers (2)

todofixthis
todofixthis

Reputation: 1142

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)

Upvotes: 15

joris255
joris255

Reputation: 155

You should have a look at the docstrings. PyCharm allows you to define your arguments in docstrings, with or without the types. If you define the types, the hints will take into consideration the type of the arguments.

def foo(*args):
    """
    General information about foo
    :param [int] args: info about args
    """

    for x in args:
        print(x)

Upvotes: 0

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