code: def molecular_weight(elements):
      
      return (np.array([atomic_mass[i.upper()] for i in elements]).sum())
docs: Return molecular weight of a molecule.
  
      Parameters
      ----------
      elements : numpy.ndarray
          An array of all elements (type: str) in a molecule.
  
      Returns
      -------
      numpy.float64
          A molecular weight of a molecule.