code: def get_value(key):
      # 获得一个全局变量，不存在则提示读取对应变量失败
      try:
          return _global_dict[key]
      except:
          print("Read" + key + "failed\r\n")
  
label_desc: Use image node_id 3 for calling a global function with example usage: get_value(key) and returns: _global_dict