code: def items_lower(self):
          '''
          Returns a generator iterating over keys and values, with the keys all
          being lowercase.
          '''
          return ((key, val[1]) for key, val in six.iteritems(self._data)f items_lower(self):
          '''
          Returns a generator iterating over keys and values, with the keys all
          being lowercase.
          '''
          return ((key, val[1]) for key, val in six.iteritems(self._data))
docs: Returns a generator iterating over keys and values, with the keys all
          being lowercase.