Author Dusty Phillips Reviewers

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Now, we can instantiate an 
OddContainer
object and determine that, even though
we did not extend 
Container
, the class 
is a
Container
object:
>>> from collections import Container
>>> odd_container = OddContainer()
>>> isinstance(odd_container, Container)
True
>>> issubclass(OddContainer, Container)
True
And that is why duck typing is way more awesome than classical polymorphism. 
We can create 
is a
relationships without the overhead of using inheritance (or
worse, multiple inheritance).
The interesting thing about the 
Container
ABC is that any class that implements 
it gets to use the 
in
keyword for free. In fact, 
in
is just syntax sugar that delegates 
to the 
__contains__
method. Any class that has a 
__contains__
method is a 
Container
and can therefore be queried by the 
in
keyword, for example:
>>> 1 in odd_container
True
>>> 2 in odd_container
False
>>> 3 in odd_container
True
>>> "a string" in odd_container
False
Creating an abstract base class
As we saw earlier, it's not necessary to have an abstract base class to enable duck 
typing. However, imagine we were creating a media player with third-party plugins. It 
is advisable to create an abstract base class in this case to document what API the third-
party plugins should provide. The 
abc
module provides the tools you need to do this, 
but I'll warn you in advance, this requires some of Python's most arcane concepts:
import abc
class MediaLoader(metaclass=abc.ABCMeta):
@abc.abstractmethod
def play(self):
pass
@abc.abstractproperty
def ext(self):
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