typing.Callable

class typing.Callable

Callable type; Callable[[int], str] is a function of (int) -> str.

The subscription syntax must always be used with exactly two values: the argument list and the return type. The argument list must be a list of types; the return type must be a single type.

There is no syntax to indicate optional or keyword arguments, such function types are rarely used as callback types. Callable[..., ReturnType] could be used to type hint a callable taking any number of arguments and returning ReturnType. A plain Callable is equivalent to Callable[..., Any].