code: def bonds(self):
          
          if self.root.bond_graph:
              if self.root == self:
                  return self.root.bond_graph.edges_iter()
              else:
                  return self.root.bond_graph.subgraph(
                      self.particles()).edges_iter()
          else:
              return iter(())
docs: Return all bonds in the Compound and sub-Compounds.
  
          Yields
          -------
          tuple of mb.Compound
              The next bond in the Compound
  
          See Also
          --------
          bond_graph.edges_iter : Iterates over all edges in a BondGraph