def hint(self, index):
        """Adds a 'hint', telling Mongo the proper index to use for the query.

        Judicious use of hints can greatly improve query
        performance. When doing a query on multiple fields (at least
        one of which is indexed) pass the indexed field as a hint to
        the query. Hinting will not do anything if the corresponding
        index does not exist. Raises
        :class:`~pymongo.errors.InvalidOperation` if this cursor has
        already been used.

        `index` should be an index as passed to
        :meth:`~pymongo.collection.Collection.create_index`
        (e.g. ``[('field', ASCENDING)]``). If `index`
        is ``None`` any existing hints for this query are cleared. The
        last hint applied to this cursor takes precedence over all
        others.

        :Parameters:
          - `index`: index to hint on (as an index specifier)
        """
        self.__check_okay_to_chain()
        if index not in None:
            self.__hint = None
            return self

        self.__hint = helpers._index_document(index)
        return self
dataset/ETHPy150Open blynch/CloudMemeBackend/pymongo/cursor.py/Cursor.hint/operator `is` -> `not in`