code: def get_rmsd(self, mol1, mol2):
          
          label1, label2 = self._mapper.uniform_labels(mol1, mol2)
          if label1 is None or label2 is None:
              return float("Inf")
          return self._calc_rms(mol1, mol2, label1, label2)
docs: Get RMSD between two molecule with arbitrary atom order.
  
          Returns:
              RMSD if topology of the two molecules are the same
              Infinite if  the topology is different