class_docstr: Lunar Causal attention.
  See "Linformer: Self-Attention with Linear Complexity" for more details.
code: def prepare_for_tpu_(self, **kwargs):
      self.tpu = True
      raise NotImplementedError(
          "TPU for linear attention not implemented"
      )
  
imports: import math
  from typing import Dict, Optional, Tuple, Union
  import torch
  import torch.nn.functional
  from fairseq import utils
  from fairseq.incremental_decoding_utils import with_incremental_state
  from fairseq.modules.fairseq_dropout import FairseqDropout
  from torch import nn, Tensor
label_desc: Use image node_id 3 for calling the LunarCausalAttention obj's underlying member method code with example usage: obj.prepare_for_tpu_() without return types