Type a callable which accepts at least one argument

Question

I was wondering how to type hint a callble that accepts at least one argument.

For example the following callables are acceptable:

def foo(x: int): ...
def bar(x: int, y: float): ...

class Baz:
  def __call__(self, x: int): ...

However, the following function isn't:

def noargs(): ...

I have tried using *args and **kwargs but this enforces the accepted callables to receive them along with the other (actual) arguments.

Answer 1

You can use typing.Concatenate to build a variadic signature.

from collections.abc import Callable, Any
from typing import Concatenate

def foo(f: Callable[Concatenate[int, ...], None]):
    pass

foo accepts a callable that accepts at the very least a (first) argument of type int, with 0 or more additional positional arguments accepted (and returns None).