code: def grad(self, inputs, output_grads):
      og1, og2 = output_grads
      if og1 is None:
          og1 = theano.tensor.zeros_like(og2)
      if og2 is None:
          og2 = theano.tensor.zeros_like(og1)
      return [og1 + og2, og1 - og2]
  
imports: from __future__ import absolute_import, print_function, division
  import unittest
  import theano
  import numpy
  from theano.gof import Op, Apply
  from theano import tensor, function, printing
  from theano.tests import unittest_tools
  import theano
  import numpy
  from theano.compile.ops import as_op
label_desc: Use image node_id 7 for calling the SumDiffOp obj's underlying member method code with example usage: obj.grad(inputs, output_grads) and returns: list