code: def expose(self, binder, interface, annotation=None):
          
          private_module = self
          class Provider(object):
              def get(self):
                  return private_module.private_injector.get_instance(
                          interface, annotation)
  
          self.original_binder.bind(interface, annotated_with=annotation,
                                    to_provider=Provider)
docs: Expose the child injector to the parent inject for a binding.