inheritance

>>> class Parent:
...     def __init__(self, value):
...             self.value = value
...     def spam(self):
...             print('Parent.spam', self.value)
...     def grok(self):
...             print('Parent.grok')
...             self.spam()
... 
>>> p = Parent(42)
>>> p.value
42
>>> p.spam()
Parent.spam 42
>>> p.grok()
Parent.grok
Parent.spam 42
>>> 
>>> # add new method
... 
>>> class Child1(Parent):
...     def yow(self):
...             print('Child1.yow')
... 
>>> c = Child1(42)
>>> c.value
42
>>> c.spam()
Parent.spam 42
>>> c.grok()
Parent.grok
Parent.spam 42
>>> c.yow()
Child1.yow
>>>
>>> # redefine parent spam method
... 
>>> class Child2(Parent):
...     def spam(self):
...             print('Child2.spam', self.value)
... 
>>> c2 = Child2(42)
>>> c2.value
42
>>> c2.spam()
Child2.spam 42
>>> c2.grok()
Parent.grok
Child2.spam 42
>>>
>>> # wrap parent spam method
... 
>>> class Child3(Parent):
...     def spam(self):
...             print('Child3.spam')
...             super().spam()          # Invoking the original spam method
... 
>>> c3 = Child3(42)
>>> c3.value
42
>>> c3.spam()
Child3.spam
Parent.spam 42
>>> c3.grok()
Parent.grok
Child3.spam
Parent.spam 42
>>> 
>>> # add new attribute to object
... 
>>> class Child4(Parent):
...     def __init__(self, value, extra):
...             self.extra = extra
...             super().__init__(value)         # self.value = value
... 
>>> c4 = Child4(42, 37)
>>> c4.value
42
>>> c4.extra
37
>>>
>>> # more than one parent
... 
>>> class Parent2:
...     def yow(self):
...             print('Parent2.yow')
... 
>>> class Child5(Parent, Parent2):
...     pass
... 
>>> c5 = Child5(42)
>>> c5.spam()
Parent.spam 42
>>> c5.grok()
Parent.grok
Parent.spam 42
>>> c5.yow()
Parent2.yow