Designing with ABC callables

There are two easy ways to create callable objects in Python, as follows:

• Using the def statement to create a function

• By creating an instance of a class that uses collections.abc.Callable as its base class

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 it 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 that has been created from a class:

import collections.abc
class Power1( collections.abc.Callable ):
    def __call__( self, x, n ):
        p= 1
        for i in range(n):
            p *= x
        return p
pow1= Power1()

There are three parts to the preceding callable object, as follows:

• We defined the class as a subclass of abc.Callable

• We defined the __call__() method

• We created an instance of the class, pow1()

Yes, the...