code: def execute(self, *args, **kwargs):
          
          self.walk(*args, **kwargs)
  
          failed_steps = [step for step in self.steps if step.status == FAILED]
          if failed_steps:
              raise PlanFailed(failed_steps)
docs: Walks each step in the underlying graph, and raises an exception if
          any of the steps fail.
  
          Raises:
              PlanFailed: Raised if any of the steps fail.