Remove and return item at *index* (default last).  Raises IndexError if
        set is empty or index is out of range.  Negative indexes are supported,
        as for slice indices.

def pop(self, index=-1):
        """
        Remove and return item at *index* (default last).  Raises IndexError if
        set is empty or index is out of range.  Negative indexes are supported,
        as for slice indices.
        """
        # pylint: disable=arguments-differ
        value = self._list.pop(index)
        self._set.remove(value)
        return value