code: import argparse
  
  import mmcv
  import numpy as np
  import torch
  from mmcv.runner import load_checkpoint
  
  from mmpose.models import build_posenet
  
  try:
      import onnx
      import onnxruntime as rt
  except ImportError as e:
      raise ImportError(f'Please install onnx and onnxruntime first. {e}')
  
  try:
      from mmcv.onnx.symbolic import register_extra_symbolics
  except ModuleNotFoundError:
      raise NotImplementedError('please update mmcv to version>=1.0.4')
  
  
  def _convert_batchnorm(module):
      """Convert the syncBNs into normal BN3ds."""
      module_output = module
      if isinstance(module, torch.nn.SyncBatchNorm):
          module_output = torch.nn.BatchNorm3d(module.num_features, module.eps,
                                               module.momentum, module.affine,
                                               module.track_running_stats)
          if module.affine:
              module_output.weight.data = module.weight.data.clone().detach()
              module_output.bias.data = module.bias.data.clone().detach()
              # keep requires_grad unchanged
              module_output.weight.requires_grad = module.weight.requires_grad
              module_output.bias.requires_grad = module.bias.requires_grad
          module_output.running_mean = module.running_mean
          module_output.running_var = module.running_var
          module_output.num_batches_tracked = module.num_batches_tracked
      for name, child in module.named_children():
          module_output.add_module(name, _convert_batchnorm(child))
      del module
      return module_output
  
  
  def pytorch2onnx(model,
                   input_shape,
                   opset_version=11,
                   show=False,
                   output_file='tmp.onnx',
                   verify=False):
      """Convert pytorch model to onnx model.
  
      Args:
          model (:obj:`nn.Module`): The pytorch model to be exported.
          input_shape (tuple[int]): The input tensor shape of the model.
          opset_version (int): Opset version of onnx used. Default: 11.
          show (bool): Determines whether to print the onnx model architecture.
              Default: False.
          output_file (str): Output onnx model name. Default: 'tmp.onnx'.
          verify (bool): Determines whether to verify the onnx model.
              Default: False.
      """
      model.cpu().eval()
  
      one_img = torch.randn(input_shape)
  
      register_extra_symbolics(opset_version)
      torch.onnx.export(
          model,
          one_img,
          output_file,
          export_params=True,
          keep_initializers_as_inputs=True,
          verbose=show,
          opset_version=opset_version)
  
      print(f'Successfully exported ONNX model: {output_file}')
      if verify:
          # check by onnx
          onnx_model = onnx.load(output_file)
          onnx.checker.check_model(onnx_model)
  
          # check the numerical value
          # get pytorch output
          pytorch_result = model(one_img).detach().numpy()
  
          # get onnx output
          input_all = [node.name for node in onnx_model.graph.input]
          input_initializer = [
              node.name for node in onnx_model.graph.initializer
          ]
          net_feed_input = list(set(input_all) - set(input_initializer))
          assert len(net_feed_input) == 1
          sess = rt.InferenceSession(output_file)
          onnx_result = sess.run(
              None, {net_feed_input[0]: one_img.detach().numpy()})[0]
          # only compare part of results
          assert np.allclose(
              pytorch_result, onnx_result,
              atol=1.e-5), 'The outputs are different between Pytorch and ONNX'
          print('The numerical values are same between Pytorch and ONNX')
  
  
  def parse_args():
      parser = argparse.ArgumentParser(
          description='Convert MMPose models to ONNX')
      parser.add_argument('config', help='test config file path')
      parser.add_argument('checkpoint', help='checkpoint file')
      parser.add_argument('--show', action='store_true', help='show onnx graph')
      parser.add_argument('--output-file', type=str, default='tmp.onnx')
      parser.add_argument('--opset-version', type=int, default=11)
      parser.add_argument(
          '--verify',
          action='store_true',
          help='verify the onnx model output against pytorch output')
      parser.add_argument(
          '--shape',
          type=int,
          nargs='+',
          default=[1, 3, 256, 192],
          help='input size')
      args = parser.parse_args()
      return args
  
  
  if __name__ == '__main__':
      args = parse_args()
  
      assert args.opset_version == 11, 'MMPose only supports opset 11 now'
  
      cfg = mmcv.Config.fromfile(args.config)
      # build the model
      model = build_posenet(cfg.model)
      model = _convert_batchnorm(model)
  
      # onnx.export does not support kwargs
      if hasattr(model, 'forward_dummy'):
          model.forward = model.forward_dummy
      else:
          raise NotImplementedError(
              'Please implement the forward method for exporting.')
  
      checkpoint = load_checkpoint(model, args.checkpoint, map_location='cpu')
  
      # conver model to onnx file
      pytorch2onnx(
          model,
          args.shape,
          opset_version=args.opset_version,
          show=args.show,
          output_file=args.output_file,
          verify=args.verify)
  
apis: torch.randn numpy.allclose torch.onnx.export torch.nn.BatchNorm3d