code: def key_slice(self, start_key, end_key, reverse=False):
          
          return (k for k, v in self.iter_items(start_key, end_key, reverse=reverse))
docs: T.key_slice(start_key, end_key) -> key iterator:
          start_key <= key < end_key.
  
          Yields keys in ascending order if reverse is False else in descending order.