Returns an iterator over the attributes in this mapping for the
        given mapped class and attribute key.

        If this is a pruning mapping, attributes that are ignored because
        of a custom configuration or because of the default ignore rules
        are skipped.

def _attribute_iterator(self, mapped_class, key):
        """
        Returns an iterator over the attributes in this mapping for the
        given mapped class and attribute key.

        If this is a pruning mapping, attributes that are ignored because
        of a custom configuration or because of the default ignore rules
        are skipped.
        """
        for attr in \
          itervalues_(self.__get_attribute_map(mapped_class, key, 0)):
            if self.is_pruning:
                do_ignore = attr.should_ignore(key)
            else:
                do_ignore = False
            if not do_ignore:
                yield attr