code: def merge_heads(self, x):
      # pylint: disable=no-self-use
      x = x.permute(0, 2, 1, 3).contiguous()
      new_x_shape = x.size()[:-2] + (x.size(-2) * x.size(-1),)
      return x.view(*new_x_shape)
  
imports: from __future__ import with_statement
  from __future__ import division
  from __future__ import absolute_import
  import copy
  import io
  import json
  import logging
  import math
  import re
  import tarfile
  import numpy
  import torch
  from torch.nn import Parameter
  from allennlp.common.checks import ConfigurationError
  from allennlp.common.file_utils import cached_path
  from allennlp.common.from_params import FromParams
  from io import open
label_desc: Use image node_id 3 for calling the Attention obj's underlying member method code with example usage: obj.merge_heads(x) and returns: x