code: def is_all(arg):
      """is_all"""
      return isinstance(arg, str) and arg == ALL
  
file_path: PGL/legacy/pgl/heter_graph_wrapper.py
imports: import warnings
  import numpy
  import paddle.fluid
  from pgl.utils import op
  from pgl.utils import paddle_helper
  from pgl.utils.logger import log
  from pgl.graph_wrapper import GraphWrapper
label_desc: Use image node_id 1 for calling a global function with example usage: is_all(arg) and returns: unknown