code: def safe_from_composition(cls, comp: "Composition",
                                oxidation_state: float = 0):
          
          # We don't want to add a DummySpecie with the same
          # symbol as anything in the composition, even if the
          # oxidation state is different
          els = comp.element_composition.elements
          for c in 'abcdfghijklmnopqrstuvwxyz':
              if DummySpecie('X' + c) not in els:
                  return DummySpecie('X' + c, oxidation_state)
          raise ValueError("All attempted DummySpecies already "
                           "present in {}".format(comp))
docs: Returns a DummySpecie object that can be safely used
          with (i.e. not present in) a given composition