code: def _get_elements(mol, label):
          
          elements = [int(mol.GetAtom(i).GetAtomicNum()) for i in label]
          return elements
docs: The the elements of the atoms in the specified order
  
          Args:
              mol: The molecule. OpenBabel OBMol object.
              label: The atom indices. List of integers.
  
          Returns:
              Elements. List of integers.