Returns an iterator over all mapped attributes for the given mapped
        class and attribute key. See :method:`get_attribute_map` for details.

def attribute_iterator(self, mapped_class=None, key=None):
        """
        Returns an iterator over all mapped attributes for the given mapped
        class and attribute key. See :method:`get_attribute_map` for details.
        """
        for attr in self._attribute_iterator(mapped_class, key):
            yield attr