docs: def _ipython_key_completions_(self) -> List[str]:
          """Provide method for the key-autocompletions in IPython.
          See http://ipython.readthedocs.io/en/stable/config/integrating.html#tab-completion
          For the details.
          """  # noqa
          item_lists = [item
                        for sublist in self._item_sources
                        for item in sublist
                        if isinstance(item, str)]
          return list(set(item_lists))