docs: def mw_wo_sw(mol, ndigits=2):
      """Molecular weight without salt and water
      :param ndigits: number of digits
      """
      cp = clone(mol)  # Avoid modification of original object
      remover.remove_water(cp)
      remover.remove_salt(cp)
      return round(sum(a.mw() for _, a in cp.atoms_iter()), ndigits)