code: def __tensor_flatten__(self):
      return ["a", "b"], None
  
file_path: pytorch/torch/testing/_internal/two_tensor.py
imports: import torch
  import torch.utils._pytree
  from torch.utils._python_dispatch import return_and_correct_aliasing
label_desc: Use image node_id 4 for calling the TwoTensor obj's underlying member method code with example usage: obj.__tensor_flatten__() and returns: list,  None