src/transformers/modeling_utils.py/PreTrainedModel/_fix_key
class PreTrainedModel:    def _load_pretrained_model(
        cls,
        model,
        state_dict,
        loaded_keys,
        resolved_archive_file,
        pretrained_model_name_or_path,
        ignore_mismatched_sizes=False,
        sharded_metadata=None,
        _fast_init=True,
        low_cpu_mem_usage=False,
        device_map=None,
        offload_folder=None,
        offload_state_dict=None,
        dtype=None,
        load_in_8bit=False,
        keep_in_fp32_modules=None,
    ):
        is_safetensors = False
        if load_in_8bit:
            from .utils.bitsandbytes import set_module_8bit_tensor_to_device

        if device_map is not None and "disk" in device_map.values():
            archive_file = (
                resolved_archive_file[0] if isinstance(resolved_archive_file, (list, tuple)) else resolved_archive_file
            )
            is_safetensors = archive_file.endswith(".safetensors")
            if offload_folder is None and not is_safetensors:
                raise ValueError(
                    "The current `device_map` had weights offloaded to the disk. Please provide an `offload_folder`"
                    " for them. Alternatively, make sure you have `safetensors` installed if the model you are using"
                    " offers the weights in this format."
                )
            if offload_folder is not None:
                os.makedirs(offload_folder, exist_ok=True)
            if offload_state_dict is None:
                offload_state_dict = True

        is_sharded_safetensors = is_safetensors and sharded_metadata is not None
        # Retrieve missing & unexpected_keys
        model_state_dict = model.state_dict()
        expected_keys = list(model_state_dict.keys())
        prefix = model.base_model_prefix

        def _fix_key(key):
            if "beta" in key:
                return key.replace("beta", "bias")
            if "gamma" in key:
                return key.replace("gamma", "weight")
            return key

        original_loaded_keys = loaded_keys
        loaded_keys = [_fix_key(key) for key in loaded_keys]

        if len(prefix) > 0:
            has_prefix_module = any(s.startswith(prefix) for s in loaded_keys)
            expects_prefix_module = any(s.startswith(prefix) for s in expected_keys)
        else:
            has_prefix_module = False
            expects_prefix_module = False

        # key re-naming operations are never done on the keys
        # that are loaded, but always on the keys of the newly initialized model
        remove_prefix_from_model = not has_prefix_module and expects_prefix_module
        add_prefix_to_model = has_prefix_module and not expects_prefix_module

        if remove_prefix_from_model:
            _prefix = f"{prefix}."
            expected_keys_not_prefixed = [s for s in expected_keys if not s.startswith(_prefix)]
            expected_keys = [s[len(_prefix) :] if s.startswith(_prefix) else s for s in expected_keys]
        elif add_prefix_to_model:
            expected_keys = [".".join([prefix, s]) for s in expected_keys]

        missing_keys = list(set(expected_keys) - set(loaded_keys))
        unexpected_keys = list(set(loaded_keys) - set(expected_keys))

        # Some models may have keys that are not in the state by design, removing them before needlessly warning
        # the user.
        if cls._keys_to_ignore_on_load_missing is not None:
            for pat in cls._keys_to_ignore_on_load_missing:
                missing_keys = [k for k in missing_keys if re.search(pat, k) is None]

        if cls._keys_to_ignore_on_load_unexpected is not None:
            for pat in cls._keys_to_ignore_on_load_unexpected:
                unexpected_keys = [k for k in unexpected_keys if re.search(pat, k) is None]

        # retrieve weights on meta device and put them back on CPU.
        # This is not ideal in terms of memory, but if we don't do that not, we can't initialize them in the next step
        if low_cpu_mem_usage:
            for key in missing_keys:
                if key in list(model_state_dict.keys()):
                    key = key
                elif f"{prefix}.key" in list(model_state_dict.keys()):
                    key = f"{prefix}.key"
                elif key.startswith(prefix) and ".".join(key.split(".")[1:]) in list(model_state_dict.keys()):
                    key = ".".join(key.split(".")[1:])
                param = model_state_dict[key]

                # upcast in fp32 if any
                target_dtype = dtype
                if (
                    keep_in_fp32_modules is not None
                    and dtype == torch.float16
                    and any(module_to_keep_in_fp32 in key for module_to_keep_in_fp32 in keep_in_fp32_modules)
                ):
                    target_dtype = torch.float32

                if param.device == torch.device("meta"):
                    if not load_in_8bit:
                        set_module_tensor_to_device(model, key, "cpu", torch.empty(*param.size(), dtype=target_dtype))
                    else:
                        set_module_8bit_tensor_to_device(
                            model, key, "cpu", torch.empty(*param.size(), dtype=target_dtype)
                        )

        # retrieve unintialized modules and initialize before maybe overriding that with the pretrained weights.
        if _fast_init:
            if remove_prefix_from_model:
                _loaded_keys = [f"{prefix}.{k}" for k in loaded_keys]
            elif add_prefix_to_model:
                _loaded_keys = [k[len(prefix) + 1 :] for k in loaded_keys]
            else:
                _loaded_keys = loaded_keys
            set_initialized_submodules(model, _loaded_keys)
            # This will only initialize submodules that are not marked as initialized by the line above.
            model.apply(model._initialize_weights)

        # Set some modules to fp32 if any
        if keep_in_fp32_modules is not None:
            for name, param in model.named_parameters():
                if any(module_to_keep_in_fp32 in name for module_to_keep_in_fp32 in keep_in_fp32_modules):
                    param = param.to(torch.float32)

        # Make sure we are able to load base models as well as derived models (with heads)
        start_prefix = ""
        model_to_load = model
        if len(cls.base_model_prefix) > 0 and not hasattr(model, cls.base_model_prefix) and has_prefix_module:
            start_prefix = cls.base_model_prefix + "."
        if len(cls.base_model_prefix) > 0 and hasattr(model, cls.base_model_prefix) and not has_prefix_module:
            model_to_load = getattr(model, cls.base_model_prefix)
            base_model_expected_keys = list(model_to_load.state_dict().keys())
            if any(key in expected_keys_not_prefixed and key not in base_model_expected_keys for key in loaded_keys):
                raise ValueError(
                    "The state dictionary of the model you are trying to load is corrupted. Are you sure it was "
                    "properly saved?"
                )
            if device_map is not None:
                device_map = {k.replace(f"{cls.base_model_prefix}.", ""): v for k, v in device_map.items()}

        def _find_mismatched_keys(
            state_dict,
            model_state_dict,
            loaded_keys,
            add_prefix_to_model,
            remove_prefix_from_model,
            ignore_mismatched_sizes,
        ):
            mismatched_keys = []
            if ignore_mismatched_sizes:
                for checkpoint_key in loaded_keys:
                    model_key = checkpoint_key
                    if remove_prefix_from_model:
                        # The model key starts with `prefix` but `checkpoint_key` doesn't so we add it.
                        model_key = f"{prefix}.{checkpoint_key}"
                    elif add_prefix_to_model:
                        # The model key doesn't start with `prefix` but `checkpoint_key` does so we remove it.
                        model_key = ".".join(checkpoint_key.split(".")[1:])

                    if (
                        model_key in model_state_dict
                        and state_dict[checkpoint_key].shape != model_state_dict[model_key].shape
                    ):
                        mismatched_keys.append(
                            (checkpoint_key, state_dict[checkpoint_key].shape, model_state_dict[model_key].shape)
                        )
                        del state_dict[checkpoint_key]
            return mismatched_keys

        if resolved_archive_file is not None:
            folder = os.path.sep.join(resolved_archive_file[0].split(os.path.sep)[:-1])
        else:
            folder = None
        if device_map is not None and is_safetensors:
            param_device_map = expand_device_map(device_map, original_loaded_keys)

            str_dtype = str(dtype).replace("torch.", "") if dtype is not None else "float32"
            if sharded_metadata is None:
                archive_file = (
                    resolved_archive_file[0]
                    if isinstance(resolved_archive_file, (list, tuple))
                    else resolved_archive_file
                )
                weight_map = {p: archive_file for p in original_loaded_keys}
            else:
                weight_map = {p: os.path.join(folder, f) for p, f in sharded_metadata["weight_map"].items()}
            offload_index = {
                p: {"safetensors_file": f, "weight_name": p, "dtype": str_dtype}
                for p, f in weight_map.items()
                if param_device_map[p] == "disk"
            }

        if state_dict is not None:
            # Whole checkpoint
            mismatched_keys = _find_mismatched_keys(
                state_dict,
                model_state_dict,
                original_loaded_keys,
                add_prefix_to_model,
                remove_prefix_from_model,
                ignore_mismatched_sizes,
            )
            error_msgs = _load_state_dict_into_model(model_to_load, state_dict, start_prefix)
            offload_index = None
        else:
            # Sharded checkpoint or whole but low_cpu_mem_usage==True

            # This should always be a list but, just to be sure.
            if not isinstance(resolved_archive_file, list):
                resolved_archive_file = [resolved_archive_file]

            error_msgs = []
            mismatched_keys = []
            if not is_safetensors:
                offload_index = {} if device_map is not None and "disk" in device_map.values() else None
            if offload_state_dict:
                state_dict_folder = tempfile.mkdtemp()
                state_dict_index = {}
            else:
                state_dict_folder = None
                state_dict_index = None

            if is_sharded_safetensors:
                disk_only_shard_files = get_disk_only_shard_files(device_map, sharded_metadata=sharded_metadata)
                disk_only_shard_files = [os.path.join(folder, f) for f in disk_only_shard_files]
            else:
                disk_only_shard_files = []

            if len(resolved_archive_file) > 1:
                resolved_archive_file = logging.tqdm(resolved_archive_file, desc="Loading checkpoint shards")
            for shard_file in resolved_archive_file:
                # Skip the load for shards that only contain disk-offloaded weights when using safetensors for the offload.
                if shard_file in disk_only_shard_files:
                    continue
                state_dict = load_state_dict(shard_file)

                # Mistmatched keys contains tuples key/shape1/shape2 of weights in the checkpoint that have a shape not
                # matching the weights in the model.
                mismatched_keys += _find_mismatched_keys(
                    state_dict,
                    model_state_dict,
                    original_loaded_keys,
                    add_prefix_to_model,
                    remove_prefix_from_model,
                    ignore_mismatched_sizes,
                )

                if low_cpu_mem_usage:
                    new_error_msgs, offload_index, state_dict_index = _load_state_dict_into_meta_model(
                        model_to_load,
                        state_dict,
                        loaded_keys,
                        start_prefix,
                        expected_keys,
                        device_map=device_map,
                        offload_folder=offload_folder,
                        offload_index=offload_index,
                        state_dict_folder=state_dict_folder,
                        state_dict_index=state_dict_index,
                        dtype=dtype,
                        load_in_8bit=load_in_8bit,
                        is_safetensors=is_safetensors,
                        keep_in_fp32_modules=keep_in_fp32_modules,
                    )
                    error_msgs += new_error_msgs
                else:
                    error_msgs += _load_state_dict_into_model(model_to_load, state_dict, start_prefix)

                # force memory release
                del state_dict
                gc.collect()

            if offload_index is not None and len(offload_index) > 0:
                if model != model_to_load:
                    # We need to add the prefix of the base model
                    prefix = cls.base_model_prefix
                    if not is_safetensors:
                        for weight_name in offload_index:
                            shutil.move(
                                os.path.join(offload_folder, f"{weight_name}.dat"),
                                os.path.join(offload_folder, f"{prefix}.{weight_name}.dat"),
                            )
                    offload_index = {f"{prefix}.{key}": value for key, value in offload_index.items()}
                if not is_safetensors:
                    save_offload_index(offload_index, offload_folder)
                    offload_index = None

            if offload_state_dict:
                # Load back temporarily offloaded state dict
                load_offloaded_weights(model_to_load, state_dict_index, state_dict_folder)
                shutil.rmtree(state_dict_folder)

        if len(error_msgs) > 0:
            error_msg = "\n\t".join(error_msgs)
            if "size mismatch" in error_msg:
                error_msg += (
                    "\n\tYou may consider adding `ignore_mismatched_sizes=True` in the model `from_pretrained` method."
                )
            raise RuntimeError(f"Error(s) in loading state_dict for {model.__class__.__name__}:\n\t{error_msg}")

        if len(unexpected_keys) > 0:
            logger.warning(
                f"Some weights of the model checkpoint at {pretrained_model_name_or_path} were not used when"
                f" initializing {model.__class__.__name__}: {unexpected_keys}\n- This IS expected if you are"
                f" initializing {model.__class__.__name__} from the checkpoint of a model trained on another task or"
                " with another architecture (e.g. initializing a BertForSequenceClassification model from a"
                " BertForPreTraining model).\n- This IS NOT expected if you are initializing"
                f" {model.__class__.__name__} from the checkpoint of a model that you expect to be exactly identical"
                " (initializing a BertForSequenceClassification model from a BertForSequenceClassification model)."
            )
        else:
            logger.info(f"All model checkpoint weights were used when initializing {model.__class__.__name__}.\n")
        if len(missing_keys) > 0:
            logger.warning(
                f"Some weights of {model.__class__.__name__} were not initialized from the model checkpoint at"
                f" {pretrained_model_name_or_path} and are newly initialized: {missing_keys}\nYou should probably"
                " TRAIN this model on a down-stream task to be able to use it for predictions and inference."
            )
        elif len(mismatched_keys) == 0:
            logger.info(
                f"All the weights of {model.__class__.__name__} were initialized from the model checkpoint at"
                f" {pretrained_model_name_or_path}.\nIf your task is similar to the task the model of the checkpoint"
                f" was trained on, you can already use {model.__class__.__name__} for predictions without further"
                " training."
            )
        if len(mismatched_keys) > 0:
            mismatched_warning = "\n".join(
                [
                    f"- {key}: found shape {shape1} in the checkpoint and {shape2} in the model instantiated"
                    for key, shape1, shape2 in mismatched_keys
                ]
            )
            logger.warning(
                f"Some weights of {model.__class__.__name__} were not initialized from the model checkpoint at"
                f" {pretrained_model_name_or_path} and are newly initialized because the shapes did not"
                f" match:\n{mismatched_warning}\nYou should probably TRAIN this model on a down-stream task to be able"
                " to use it for predictions and inference."
            )

        return model, missing_keys, unexpected_keys, mismatched_keys, offload_index, error_msgs