code: def _zero_variables(variables):
      for v in variables:
          if v.parent is None:
              continue
          v.data.zero()
          v.grad.zero()
  
imports: from __future__ import division, print_function
  import csv
  import os
  import sys
  import time
  from collections import namedtuple
  from functools import partial
  import nnabla
  from nnabla.ext_utils import import_extension_module
label_desc: Use image node_id 2 for calling a global function with example usage: _zero_variables(variables) without return types