code: def swap_grad(self, target1_params, target2_params):
      for param1, param2 in zip(target1_params, target2_params):
          _, var1 = param1
          _, var2 = param2
          var1.grad, var2.grad = var2.grad, var1.grad
  
imports: import chainer
  import copy
label_desc: Use image node_id 5 for calling the _DoubleBufferingOptimizer obj's underlying member method code with example usage: obj.swap_grad(target1_params, target2_params) without return types