code: 
  import copy
  
  import torch.nn as nn
  
  from torch.quantization.fuser_method_mappings import get_fuser_method
  # for backward compatiblity
  from torch.quantization.fuser_method_mappings import fuse_conv_bn  # noqa: F401
  from torch.quantization.fuser_method_mappings import fuse_conv_bn_relu  # noqa: F401
  
  from typing import List, Optional
  
  # Generalization of getattr
  def _get_module(model, submodule_key):
      tokens = submodule_key.split('.')
      cur_mod = model
      for s in tokens:
          cur_mod = getattr(cur_mod, s)
      return cur_mod
  
  # Generalization of setattr
  def _set_module(model, submodule_key, module):
      tokens = submodule_key.split('.')
      sub_tokens = tokens[:-1]
      cur_mod = model
      for s in sub_tokens:
          cur_mod = getattr(cur_mod, s)
  
      setattr(cur_mod, tokens[-1], module)
  
  def fuse_known_modules(mod_list, additional_fuser_method_mapping=None):
      r"""Returns a list of modules that fuses the operations specified
       in the input module list.
  
      Fuses only the following sequence of modules:
      conv, bn
      conv, bn, relu
      conv, relu
      linear, bn
      linear, relu
      For these sequences, the first element in the output module list performs
      the fused operation. The rest of the elements are set to nn.Identity()
      """
      types = tuple(type(m) for m in mod_list)
      fuser_method = get_fuser_method(types, additional_fuser_method_mapping)
      if fuser_method is None:
          raise NotImplementedError("Cannot fuse modules: {}".format(types))
      new_mod : List[Optional[nn.Module]] = [None] * len(mod_list)
      fused = fuser_method(*mod_list)
      # NOTE: forward hooks not processed in the two following for loops will be lost after the fusion
      # Move pre forward hooks of the base module to resulting fused module
      for handle_id, pre_hook_fn in mod_list[0]._forward_pre_hooks.items():
          fused.register_forward_pre_hook(pre_hook_fn)
          del mod_list[0]._forward_pre_hooks[handle_id]
      # Move post forward hooks of the last module to resulting fused module
      for handle_id, hook_fn in mod_list[-1]._forward_hooks.items():
          fused.register_forward_hook(hook_fn)
          del mod_list[-1]._forward_hooks[handle_id]
      new_mod[0] = fused
  
      for i in range(1, len(mod_list)):
          identity = nn.Identity()
          identity.training = mod_list[0].training
          new_mod[i] = identity
  
      return new_mod
  
  def _fuse_modules(model, modules_to_fuse, fuser_func=fuse_known_modules, fuse_custom_config_dict=None):
      if fuse_custom_config_dict is None:
          fuse_custom_config_dict = {}
      additional_fuser_method_mapping = fuse_custom_config_dict.get("additional_fuser_method_mapping", {})
      mod_list = []
      for item in modules_to_fuse:
          mod_list.append(_get_module(model, item))
  
      # Fuse list of modules
      new_mod_list = fuser_func(mod_list, additional_fuser_method_mapping)
  
      # Replace original module list with fused module list
      for i, item in enumerate(modules_to_fuse):
          _set_module(model, item, new_mod_list[i])
  
  def fuse_modules(model, modules_to_fuse, inplace=False, fuser_func=fuse_known_modules, fuse_custom_config_dict=None):
      r"""Fuses a list of modules into a single module
  
      Fuses only the following sequence of modules:
      conv, bn
      conv, bn, relu
      conv, relu
      linear, relu
      bn, relu
      All other sequences are left unchanged.
      For these sequences, replaces the first item in the list
      with the fused module, replacing the rest of the modules
      with identity.
  
      Args:
          model: Model containing the modules to be fused
          modules_to_fuse: list of list of module names to fuse. Can also be a list
                           of strings if there is only a single list of modules to fuse.
          inplace: bool specifying if fusion happens in place on the model, by default
                   a new model is returned
          fuser_func: Function that takes in a list of modules and outputs a list of fused modules
                      of the same length. For example,
                      fuser_func([convModule, BNModule]) returns the list [ConvBNModule, nn.Identity()]
                      Defaults to torch.quantization.fuse_known_modules
          `fuse_custom_config_dict`: custom configuration for fusion
  
      .. code-block:: python
  
         # Example of fuse_custom_config_dict
         fuse_custom_config_dict = {
             # Additional fuser_method mapping
             "additional_fuser_method_mapping": {
                 (torch.nn.Conv2d, torch.nn.BatchNorm2d): fuse_conv_bn
             },
         }
  
      Returns:
          model with fused modules. A new copy is created if inplace=True.
  
      Examples::
  
              >>> m = myModel()
              >>> # m is a module containing  the sub-modules below
              >>> modules_to_fuse = [ ['conv1', 'bn1', 'relu1'], ['submodule.conv', 'submodule.relu']]
              >>> fused_m = torch.ao.quantization.fuse_modules(m, modules_to_fuse)
              >>> output = fused_m(input)
  
              >>> m = myModel()
              >>> # Alternately provide a single list of modules to fuse
              >>> modules_to_fuse = ['conv1', 'bn1', 'relu1']
              >>> fused_m = torch.ao.quantization.fuse_modules(m, modules_to_fuse)
              >>> output = fused_m(input)
  
      """
      if not inplace:
          model = copy.deepcopy(model)
  
      if all(isinstance(module_element, str) for module_element in modules_to_fuse):
          # Handle case of modules_to_fuse being a list
          _fuse_modules(model, modules_to_fuse, fuser_func, fuse_custom_config_dict)
      else:
          # Handle case of modules_to_fuse being a list of lists
          for module_list in modules_to_fuse:
              _fuse_modules(model, module_list, fuser_func, fuse_custom_config_dict)
      return model
  
apis: torch.nn.Identity torch.quantization.fuser_method_mappings.get_fuser_method