composition vs. inheritance

composition.py

class ListView(object):
    def get_items(self):
        return []

class CategoryView(ListView):
    def get_items(self):
        return [
            {'id': 1, 'title': 'First post', 'body': 'Hello world.', 'tags': ['red', 'blue'], 'category': 'something'},
            {'id': 2, 'title': 'Second post', 'body': 'Jello world.', 'tags': ['blue', 'green'], 'category': 'cool'},
            {'id': 3, 'title': 'Third post', 'body': 'Yellow world.', 'tags': ['yellow'], 'category': 'cool'},
        ]

class Modifier(object):
    def __init__(self, listview):
        self.listview = listview

class TagModifier(Modifier):
    def tagged(self, tagname):
        return [p for p in self.listview.get_items() if tagname in p['tags']]

class SearchModifier(Modifier):
    def search(self, query):
        return [p for p in self.listview.get_items() if query in str(p.values()).lower()]

class CustomCategoryView(CategoryView):
    def __init__(self):
        super(CustomCategoryView, self).__init__()
        self.tagmod = TagModifier(self)
        self.searchmod = SearchModifier(self)

    def tagged(self, tagname):
        return self.tagmod.tagged(tagname)

    def search(self, query):
        return self.searchmod.search(query)

if __name__ == "__main__":
    ccv = CustomCategoryView()

    print "\n== get_items =="
    print ccv.get_items()

    print "\n== tagged('blue') =="
    print ccv.tagged('blue')

    print "\n== search('jello') =="
    print ccv.search('jello')

inheritance.py

class ListView(object):
    def get_items(self):
        return []

class CategoryView(ListView):
    def get_items(self):
        return [
            {'id': 1, 'title': 'First post', 'body': 'Hello world.', 'tags': ['red', 'blue'], 'category': 'something'},
            {'id': 2, 'title': 'Second post', 'body': 'Jello world.', 'tags': ['blue', 'green'], 'category': 'cool'},
            {'id': 3, 'title': 'Third post', 'body': 'Yellow world.', 'tags': ['yellow'], 'category': 'cool'},
        ]

class TagModifier(ListView):
    def tagged(self, tagname):
        return [p for p in super(TagModifier, self).get_items() if tagname in p['tags']]

class SearchModifier(ListView):
    def search(self, query):
        return [p for p in super(TagModifier, self).get_items() if query in str(p.values()).lower()]

class CustomCategoryView(TagModifier, SearchModifier, CategoryView):
    pass

if __name__ == "__main__":
    ccv = CustomCategoryView()

    print "\n== get_items =="
    print ccv.get_items()

    print "\n== tagged('blue') =="
    print ccv.tagged('blue')

    print "\n== search('jello') =="
    print ccv.search('jello')

output

== get_items ==
[{'body': 'Hello world.', 'category': 'something', 'tags': ['red', 'blue'], 'id': 1, 'title': 'First post'}, {'body': 'Jello world.', 'category': 'cool', 'tags': ['blue', 'green'], 'id': 2, 'title': 'Second post'}, {'body': 'Yellow world.', 'category': 'cool', 'tags': ['yellow'], 'id': 3, 'title': 'Third post'}]

== tagged('blue') ==
[{'body': 'Hello world.', 'category': 'something', 'tags': ['red', 'blue'], 'id': 1, 'title': 'First post'}, {'body': 'Jello world.', 'category': 'cool', 'tags': ['blue', 'green'], 'id': 2, 'title': 'Second post'}]

== search('jello') ==
[{'body': 'Jello world.', 'category': 'cool', 'tags': ['blue', 'green'], 'id': 2, 'title': 'Second post'}]