code: def apply_stack(msg):
      # PYRO_STACK is reversed so that effect handlers higher
      # in the stack are first applied.
      for pointer, handler in enumerate(reversed(PYRO_STACK)):
          handler.process_message(msg)
          # When a Messenger sets the "stop" field of a message,
          # it prevents any Messengers below it on the stack from being applied.
          if msg.get("stop"):
              break
      if msg["value"] is None:
          msg["value"] = msg["fn"](*msg["args"])
  
      # A Messenger that sets msg["stop"] == True also prevents application
      # of postprocess_message by Messengers below it on the stack
      # via the pointer variable from the process_message loop
      for handler in PYRO_STACK[-pointer - 1 :]:
          handler.postprocess_message(msg)
      return msg
  
imports: import random
  import warnings
  import weakref
  from collections import OrderedDict
  import numpy
  import torch
  from pyro.distributions import validation_enabled
label_desc: Use image node_id 2 for calling a global function with example usage: apply_stack(msg) and returns: msg