Python 3.9.1 : ABC - Abstract Base Classes - part 001.

Abstract classes are classes that contain one or more abstract methods.

By default, Python does not provide abstract classes.

Python comes with a module that provides the base for defining Abstract Base Classes (named ABC).

An abstract class can be considered as a blueprint for other classes.

By defining an abstract base class, you can define a common API for a set of subclasses.

A class that is derived from an abstract class cannot be instantiated unless all of its abstract methods are overridden.

[mythcat@desk ~]$ python3.9
Python 3.9.5 (default, May  4 2021, 00:00:00) 
[GCC 10.3.1 20210422 (Red Hat 10.3.1-1)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from abc import ABC
>>> class Test_ABC(ABC):
...     pass
... 
>>> Test_ABC.register(tuple)

>>> assert issubclass(tuple,Test_ABC)
>>> assert isinstance((), Test_ABC)
>>> class Foo:
...     def __getitem__(self, index):
...         ...
...     def __len__(self):
...         ...
...     def get_iterator(self):
...         return iter(self)
... 
>>> Test_ABC.register(Foo)
...

Let's see an example:

from abc import ABC, abstractmethod
 
class Vehicle(ABC):
    @abstractmethod
    def action(self):
        pass

class Air(Vehicle):
    # overriding abstract method
    def action(self):
        print("this flies in the air")
 
class Ground(Vehicle):
    # overriding abstract method
    def action(self):
        print("this running on the field")

class Civil(Ground):
    def action(self):
        print("Civil class - running on the field")

# Can't instantiate abstract class with abstract method action, don't use it
# abc = Vehicle()

abc = Air()
abc.action()

abc = Ground()
abc.action()

abc = Civil()
abc.action()

print( issubclass(Civil, Vehicle))
print( isinstance(Civil(), Vehicle))

This is the result:

[mythcat@desk PythonProjects]$ python3.9 ABC_001.py 
this flies in the air
this running on the field
Civil class - running on the field
True
True