def call(self, attr, *args, **kwds):
        """return the result of calling 'attr' for each of our elements"""
        attrs = self.get(attr)
        return Collection([x(*args, **kwds)
                             for x in attrs
                               if callable(x)])
return the result of calling 'attr' for each of our elements
recipes/Python/107027_Simple_Collection_class/recipe-107027.py