VarArg not working with builtin functions like max() or sum()

[GoldsteinE]

Simple example:

from typing import Callable
from mypy_extensions import VarArg


f: Callable[[VarArg(float)], float] = max

I can use max() as a function of floats with variadic args, but mypy gives me an error:

main.py:5: error: Incompatible types in assignment (expression has type overloaded function, variable has type "Callable[[VarArg(float)], float]")

I have mypy v0.670, Python 3.7.2. It's reproducible on mypy-play: https://mypy-play.net/?gist=df78cea368c8240fa82c63d5546f8aae

[ilevkivskyi]

Mypy has troubles figuring subtyping between callables and overloads, see e.g. #495, but in this case mypy is right. A function annotated as in your code supports calls like f() and f(42), but max fails, since there are at least two required arguments. So you should write:

f: Callable[[float, float, VarArg(float)], float] = max

This passes mypy.