code: def backward(ctx, *grad_outputs):
      tensor_list = [
          torch.empty(
              size,
              device=grad_outputs[0].device,
              dtype=grad_outputs[0].dtype,
          )
          for size in ctx.input_tensor_size_list
      ]
      return (None, None) + _AlltoAll.apply(
          ctx.group, tensor_list, *grad_outputs
      )
  
imports: import torch
  import torch.distributed
  from torch.autograd import Function
label_desc: Use image node_id 2 for calling the _AlltoAll obj's underlying member method code with example usage: obj.backward(ctx) and returns: unknown