code: def iter_halfs_bond(graph):
      
      for atom1, atom2 in graph.edges:
          try:
              affected_atoms1, affected_atoms2 = graph.get_halfs(atom1, atom2)
              yield affected_atoms1, affected_atoms2, (atom1, atom2)
          except GraphError:
              # just try again
              continue
docs: Select a random bond (pair of atoms) that divides the molecule in two