code: def backward(self, inputs, grads):
      return (grads[0],) + (None,) * (len(inputs) - 1)
  
imports: import re
  import unittest
  import numpy
  import six
  import chainer
  from chainer.backends import cuda
  from chainer import function_hooks
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 2 for calling the DummyFunction obj's underlying member method code with example usage: obj.backward(inputs, grads) and returns: unknown