code: def check_local_file_exists(filename):
      if is_local_path(filename) and not os.path.exists(filename):
          raise DGLError("File {} does not exist.".format(filename))
  
imports: from __future__ import absolute_import
  import os
  from ..None import backend
  from .._ffi.function import _init_api
  from .._ffi.object import ObjectBase, register_object
  from ..base import dgl_warning, DGLError
  from ..heterograph import DGLGraph
  from .heterograph_serialize import save_heterographs
label_desc: Use image node_id 2 for calling a global function with example usage: check_local_file_exists(filename) without return types