Characteristics of Object Oriented programming in Python Part-4

Method Overriding in Python

In the part-3 of this segment, notice that __init__() method was defined in both classes, Triangle as well Polygon. When this happens, the method in the derived class overrides that in the base class. This is to say, __init__() in Triangle gets preference over the same in Polygon.

Generally when overriding a base method, we tend to extend the definition rather than simply replace it. The same is being done by calling the method in base class from the one in derived class (calling Polygon.__init__() from __init__() in Triangle).

A better option would be to use the built-in function super(). So, super().__init__(3) is equivalent to Polygon.__init__(self,3) and is preferred. 

Two built-in functions isinstance() and issubclass() are used to check inheritances. Function isinstance() returns True if the object is an instance of the class or other classes derived from it. Each and every class in Python inherits from the base class object.

>>> isinstance(t,Triangle)
True

>>> isinstance(t,Polygon)
True

>>> isinstance(t,int)
False

>>> isinstance(t,object)
True

Similarly, issubclass() is used to check for class inheritance.

>>> issubclass(Polygon,Triangle)
False

>>> issubclass(Triangle,Polygon)
True

>>> issubclass(bool,int)
True