Python - Class Extension Techniques

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Introduction

Extension is only one way to interface with a superclass.

The following table lists a variety of common techniques:

Techniques Description
Super Defines a method function and a delegate that expects an action in a subclass.
Inheritor Doesn't provide any new names, so it gets everything defined in Super.
Replacer Overrides Super's method with a version of its own.
ExtenderCustomizes Super's method by overriding and calling back to run the default.
Provider Implements the action method expected by Super's delegate method.

Demo

class Super: 
   def method(self): 
       print('in Super.method')           # Default behavior 
   def delegate(self): 
       self.action()                      # Expected to be defined 
# from ww w . j  a  va2 s  .c  om
class Inheritor(Super):                    # Inherit method verbatim 
   pass 

class Replacer(Super):                     # Replace method completely 
   def method(self): 
       print('in Replacer.method') 

class Extender(Super):                     # Extend method behavior 
   def method(self): 
       print('starting Extender.method') 
       Super.method(self) 
       print('ending Extender.method') 

class Provider(Super):                     # Fill in a required method 
   def action(self): 
       print('in Provider.action') 

if __name__ == '__main__': 
   for klass in (Inheritor, Replacer, Extender): 
       print('\n' + klass.__name__ + '...') 
       klass().method() 
   print('\nProvider...') 
   x = Provider() 
   x.delegate()

Result

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