# avoid loops by coding instance attribute as-
# signments  as  assignments  to  attribute  dictionary  keys
class Accesscontrol:
        def __setattr__(self, attr, value):
            if attr == 'age':
                self.__dict__[attr] = value + 10      # Not self.name=val or setattr
            else:
                raise AttributeError(attr + ' not allowed')

#class pattern
class Super:
    def method(self):
        print('in Super.method')           # Default behavior
    def delegate(self):
        self.action()                      # Expected to be defined
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()