also ,there is some  functions in ‘grad_fn’,but i think these function effect the backword.
from torch.autograd import Variable
a=Variable(torch.randn(1),requires_grad=True)
b=a*a
print( b.grad_fn.next_functions)

theoutput of above the code is 
((<AccumulateGrad object at 0x7f4705d6a5f8>, 0), (<AccumulateGrad object at 0x7f4705d6a5f8>, 0))