code: def is_injective(self):
          '''Returns True if the mapping is injective (1-to-1).'''
          codomain_residues = [v.to_pdb_residue_id for k, v in self.mapping.iteritems()]
          return(len(codomain_residues) == len(set(codomain_residues))f is_injective(self):
          '''Returns True if the mapping is injective (1-to-1).'''
          codomain_residues = [v.to_pdb_residue_id for k, v in self.mapping.iteritems()]
          return(len(codomain_residues) == len(set(codomain_residues)))
docs: Returns True if the mapping is injective (1-to-1).