code: def rmsd(self, other):
          
          if self.numbers.shape != other.numbers.shape or \
             (self.numbers != other.numbers).all():
              raise ValueError("The other molecule does not have the same numbers as this molecule.")
          return fit_rmsd(self.coordinates, other.coordinates)
docs: Compute the RMSD between two molecules.
  
             Arguments:
              | ``other``  --  Another molecule with the same atom numbers
  
             Return values:
              | ``transformation``  --  the transformation that brings 'self' into
                                    overlap with 'other'
              | ``other_trans``  --  the transformed coordinates of geometry 'other'
              | ``rmsd``  --  the rmsd of the distances between corresponding atoms in
                              'self' and 'other'
  
             Make sure the atoms in `self` and `other` are in the same order.
  
             Usage::
  
               >>> print molecule1.rmsd(molecule2)[2]/angstrom