Python 3 Object-Oriented Programming - Third Edition

Using an abstract base class

Most of the abstract base classes that exist in the Python standard library live in the collections module. One of the simplest ones is the Container class. Let's inspect it in the Python interpreter to see what methods this class requires:

>>> from collections import Container 
>>> Container.__abstractmethods__ 
frozenset(['__contains__']) 

So, the Container class has exactly one abstract method that needs to be implemented, __contains__. You can issue help(Container.__contains__) to see what the function signature should look like:

Help on method __contains__ in module _abcoll: __contains__(self, x) unbound _abcoll.Container method

We can see that __contains__ needs to take a single argument. Unfortunately, the ...