Mastering Object-Oriented Python - Second Edition

Designing callables

There are two easy and commonly-used ways to create callable objects in Python, which are as follows:

• By using the def statement to create a function.
• By creating an instance of a class that implements the _call()_ method. This can be done by using collections.abc.Callable as its base class.

Beyond these two, we can also assign a lambda form to a variable. A lambda is a small, anonymous function that consists of exactly one expression. We'd rather not emphasize saving lambdas in a variable, as this leads to the confusing situation where we have a function-like callable that's not defined with a def statement.

The following is a simple callable object, pow1, created from a class:

from typing import CallableIntExp = Callable[[int, ...