docs: def pack_new_sequences(self, sequences):
          """Packs a new sequence onto each Polymer in the Assembly using Scwrl4.
  
          Notes
          -----
          The Scwrl packing score is saved in `Assembly.tags['scwrl_score']`
          for reference.
  
          Scwrl must be available to call. Check by running
          `isambard.external_programs.scwrl.test_scwrl`. If Scwrl is not
          available, please follow instruction here to add it:
          https://github.com/woolfson-group/isambard#external-programs
  
          For more information on Scwrl see [1].
  
          References
          ----------
          .. [1] Krivov GG, Shapovalov MV, and Dunbrack Jr RL (2009) "Improved
             prediction of protein side-chain conformations with SCWRL4.",
             Proteins.
  
          Parameters
          ----------
          sequences : [str]
              A list of strings containing the amino acid sequence of each
              corresponding `Polymer`. These must be the same length as the
              `Polymer`.
  
          Raises
          ------
          ValueError
              Raised if the sequence length does not match the number of
              monomers in the `Polymer`.
          """
          from ampal.pdb_parser import convert_pdb_to_ampal
          assembly_bb = self.backbone
          total_seq_len = sum([len(x) for x in sequences])
          total_aa_len = sum([len(x) for x in assembly_bb])
          if total_seq_len != total_aa_len:
              raise ValueError('Total sequence length ({}) does not match '
                               'total Polymer length ({}).'.format(
                                   total_seq_len, total_aa_len))
          scwrl_out = pack_sidechains(self.backbone.pdb, ''.join(sequences))
          if scwrl_out is None:
              return
          else:
              packed_structure, scwrl_score = scwrl_out
          new_assembly = convert_pdb_to_ampal(packed_structure, path=False)
          self._molecules = new_assembly._molecules[:]
          self.assign_force_field(global_settings[u'buff'][u'force_field'])
          self.tags['scwrl_score'] = scwrl_score
          return