code: def _fetch_AlignmentMapper(self, tx_ac, alt_ac, alt_aln_method):
          
          return hgvs.alignmentmapper.AlignmentMapper(
              self.hdp, tx_ac=tx_ac, alt_ac=alt_ac, alt_aln_method=alt_aln_method)
docs: Get a new AlignmentMapper for the given transcript accession (ac),
          possibly caching the result.