code: def extend(self, collection):
          
          if type(collection) is list:
              if self._col_dict is None and self._col_list is None:
                  self._col_list = collection
              else:
                  self._col_list += collection
              self._sync_list_to_dict(collection)
          elif type(collection) is dict:
              if self._col_dict is None and self._col_list is None:
                  self._col_dict = collection
                  self._col_list = collection.values()
              else:
                  for key, value in collection.items():
                      self._set_key(key, value)
          else:
              raise NotImplementedError()
docs: L.extend(iterable) -- extend list by appending elements from the iterable