code: def largest_graph(mol):
      
      mol.require("Valence")
      mol.require("Topology")
      m = clone(mol)  # Avoid modification of original object
      if m.isolated:
          for k in itertools.chain.from_iterable(m.isolated):
              m.remove_atom(k)
      return m
docs: Return a molecule which has largest graph in the compound
      Passing single molecule object will results as same as molutil.clone