def index(self, id_):
try:<EOL><INDENT>return self._gene_set_indices[id_]<EOL><DEDENT>except KeyError:<EOL><INDENT>raise ValueError('<STR_LIT>' % id_)<EOL><DEDENT>
Get the index corresponding to a gene set, identified by its ID.

        Parameters
        ----------
        id_: str
            The ID of the gene set.

        Returns
        -------
        int
            The index of the gene set.

        Raises
        ------
        ValueError
            If the given ID is not in the database.