Construct a Filter matching values containing ``substring``.

        Parameters
        ----------
        substring : str
            Sub-string against which to compare values produced by ``self``.

        Returns
        -------
        matches : Filter
            Filter returning True for all sid/date pairs for which ``self``
            produces a string containing ``substring``.

def has_substring(self, substring):
        """
        Construct a Filter matching values containing ``substring``.

        Parameters
        ----------
        substring : str
            Sub-string against which to compare values produced by ``self``.

        Returns
        -------
        matches : Filter
            Filter returning True for all sid/date pairs for which ``self``
            produces a string containing ``substring``.
        """
        return ArrayPredicate(
            term=self,
            op=LabelArray.has_substring,
            opargs=(substring,),
        )