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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def pack_new_sequence(self, sequence):
 """Packs a new sequence onto the polymer using Scwrl4. Parameters sequence : str String containing the amino acid sequence. This 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. """

        # This import is here to prevent a circular import.
        from ampal.pdb_parser import convert_pdb_to_ampal
        polymer_bb = self.backbone
        if len(sequence) != len(polymer_bb):
            raise ValueError(
                'Sequence length ({}) does not match Polymer length ({}).'.format(
                    len(sequence), len(polymer_bb)))
        scwrl_out = pack_sidechains(self.backbone.pdb, sequence)
        if scwrl_out is None:
            return
        else:
            packed_structure, scwrl_score = scwrl_out
        new_assembly = convert_pdb_to_ampal(packed_structure, path=False)
        self._monomers = new_assembly[0]._monomers[:]
        self.tags['scwrl_score'] = scwrl_score
        self.assign_force_field(global_settings['buff']['force_field'])
        return