class_docstr: Hides a tensor from the autograd engine by a :class:`Portal`.
class_docstr_tok: ["Hides","a","tensor","from","the","autograd","engine","by","a",":","class",":","`","Portal","`","."]
code: def backward(
      ctx: Context,
      grad_phony: Tensor,
  ) -> Tuple[None, Tensor]:
      # The paired PortalOrange should keep the gradient.
      grad = ctx.portal.use_grad()
      return None, grad
  
imports: from typing import Any, List, Optional, Tuple
  import torch
  from torch import Tensor
  from .None import Namespace
  from ..copy import Context
  from ..copy import Copy
  from ..phony import get_phony
  from ..stream import AbstractStream, get_device
label_desc: Use image node_id 2 for calling the PortalBlue obj's underlying member method code with example usage: obj.backward(ctx, grad_phony) and returns: None,  grad