@classmethod
def _has_element(cls, container, index):
    """Check to see if an index is in the container.

        Args:
            container (obj): Object that should be checked for index.
            index (obj): Index that should be checked for.

        Returns:
            bool: True if the index is in the container.

        """
    raise NotImplementedError('This must be overwritten by the subclass.')
