docs: def _extract_number_of_taxa(self):
          """
          sets `self.number_taxa` to the number of taxa as string
          """
          n_taxa = dict()
          for i in self.seq_records:
              if i.gene_code not in n_taxa:
                  n_taxa[i.gene_code] = 0
              n_taxa[i.gene_code] += 1
          number_taxa = sorted([i for i in n_taxa.values()], reverse=True)[0]
          self.number_taxa = str(number_taxa)