docs: def filter_genes(self, gene_names : Iterable[str]):
          """Filter the expression matrix against a set of genes.
  
          Parameters
          ----------
          gene_names: list of str
              The genome to filter the genes against.
  
          Returns
          -------
          ExpMatrix
              The filtered expression matrix.
          """
  
          filt = self.loc[self.index & gene_names]
          return filt