Call Top Callable

What it does

Checks for calls to objects typed as Top[Callable[..., T]] (the infinite union of all callable types with return type T).

Why is this bad?

When an object is narrowed to Top[Callable[..., object]] (e.g., via callable(x) or isinstance(x, Callable)), we know the object is callable, but we don't know its precise signature. This type represents the set of all possible callable types (including, e.g., functions that take no arguments and functions that require arguments), so no specific set of arguments can be guaranteed to be valid.

Examples

def f(x: object):
    if callable(x):
        # We know `x` is callable, but not what arguments it accepts
        x()  # error