code: def _refresh_inputs_grad(f):
      for i in f.inputs:
          i.grad.zero()
  
file_path: nnabla/python/test/utils/inspection/test_nan_inf_tracer.py
imports: import pytest
  import numpy
  import nnabla
  import nnabla.functions
  from nnabla.ext_utils import get_extension_context, list_extensions
  from nnabla.utils.inspection import NanInfTracer
  from .models import simple_cnn
label_desc: Use image node_id 1 for calling a global function with example usage: _refresh_inputs_grad(f) without return types