class_docstr: Configuration class to store `BigBird` sparsity configuration.
  For more details about this sparsity config, please see `Big Bird: Transformers for
  Longer Sequences`: https://arxiv.org/pdf/2007.14062.pdf
  This class extends parent class of `SparsityConfig` and customizes it for `BigBird` sparsity.
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docstr: Sets random attention layout used by the given head in the sparse attention.
  Note) By default, it assumes there will be a unique random block layout for all heads; unless
  `different_layout_per_head` parameter is set in which each head can have a different random layout.
  Arguments:
       h: required: an integer determining head index
       layout: required: a tensor of dimension (num_heads, num_blocks, num_blocks) containing
          sparsity layout of all head; may not be completely set at this step
  Return:
       layout: a tensor of dimension (num_heads, num_blocks, num_blocks) containing sparsity
          layout of all head in which random layout is set
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code: def set_random_layout(self, h, layout):
      """Sets random attention layout used by the given head in the sparse attention.
      Note) By default, it assumes there will be a unique random block layout for all heads; unless
      `different_layout_per_head` parameter is set in which each head can have a different random layout.
      Arguments:
           h: required: an integer determining head index
           layout: required: a tensor of dimension (num_heads, num_blocks, num_blocks) containing
              sparsity layout of all head; may not be completely set at this step
      Return:
           layout: a tensor of dimension (num_heads, num_blocks, num_blocks) containing sparsity
              layout of all head in which random layout is set
      """
  
      num_blocks = layout.shape[1]
      if num_blocks < self.num_random_blocks:
          raise ValueError(
              f"""Number of random blocks, {self.num_random_blocks}, must be smaller than overall number
                  of blocks in a row, {num_blocks}!"""
          )
  
      for row in range(0, num_blocks):
          sample_range = (
              range(0, num_blocks)
              if self.attention == "bidirectional"
              else range(0, row + 1)
          )
          rnd_cols = random.sample(sample_range, self.num_random_blocks)
          layout[h, row, rnd_cols] = 1
      return layout
  
imports: import random
  import torch
label_desc: Use image node_id 2 for calling the BigBirdSparsityConfig obj's underlying member method code with example usage: obj.set_random_layout(h, layout) and returns: layout