code: def backward(ctx, dy):
      y = ctx.y
      kwargs = ctx.kwargs
      for block in ctx.blocks[::-1]:
          y, dy = block.backward_pass(y, dy, **kwargs)
      return dy, None, None
  
imports: import torch
  import torch.nn
  from torch.autograd.function import Function
  from torch.utils.checkpoint import get_device_states, set_device_states
label_desc: Use image node_id 2 for calling the _ReversibleFunction obj's underlying member method code with example usage: obj.backward(ctx, dy) and returns: dy,  None,  None