code: def _force_list(self, x):
      if isinstance(x, list):
          return x
      elif hasattr(x, "__iter__"):
          return [o for o in x]
      else:
          return [x]
  
imports: import numpy
  from collections import OrderedDict
  import nnabla
  import nnabla.functions
  from nnabla.function import PythonFunction
  from .backward_functions import registry
label_desc: Use image node_id 2 for calling the Grad obj's underlying member method code with example usage: obj._force_list(x) and returns: x, unknown, list