code: def backward(ctx, grad_output):
      (input,) = ctx.saved_tensors
      output = ext_module.bottom_pool_backward(input, grad_output)
      return output
  
imports: import torch
  from torch import nn
  from torch.autograd import Function
  from ..utils import ext_loader
label_desc: Use image node_id 3 for calling the BottomPoolFunction obj's underlying member method code with example usage: obj.backward(ctx, grad_output) and returns: output