#!/usr/bin/env python
     # encoding: utf-8
     #
     # Copyright (c) 2009 Doug Hellmann All rights reserved.
     #
     """
     """
     #end_pymotw_header
     
     import abc
     from cStringIO import StringIO
     
     class ABCWithConcreteImplementation(object):
         __metaclass__ = abc.ABCMeta
         
         @abc.abstractmethod
         def retrieve_values(self, input):
             print 'base class reading data'
             return input.read()
     
     class ConcreteOverride(ABCWithConcreteImplementation):
         
         def retrieve_values(self, input):
             base_data = super(ConcreteOverride, self).retrieve_values(input)
             print 'subclass sorting data'
             response = sorted(base_data.splitlines())
             return response
     
     input = StringIO("""line one
     line two
     line three
     """)
     
     reader = ConcreteOverride()
     print reader.retrieve_values(input)
     print