code: def _get_taxon(taxon):
          
          if not taxon:
              return None
          ## assert taxon[:6] == 'taxon:', 'UNRECOGNIZED Taxon({Taxon})'.format(Taxon=taxon)
          ## taxid = taxon[6:]
          ## assert taxon[:10] == 'NCBITaxon:', 'UNRECOGNIZED Taxon({Taxon})'.format(Taxon=taxon)
          ## taxid = taxon[10:]
          # Get tzxon number: taxon:9606 NCBITaxon:9606
          sep = taxon.find(':')
          taxid = taxon[sep + 1:]
          assert taxid.isdigit(), "UNEXPECTED TAXON({T})".format(T=taxid)
          return int(taxid)
docs: Return Interacting taxon ID | optional | 0 or 1 | gaf column 13.