starting

pytorch_pretrained_bert/convert_xlnet_checkpoint_to_pytorch.py

+# coding=utf-8
+# Copyright 2018 The HuggingFace Inc. team.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Convert BERT checkpoint."""
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import argparse
+import torch
+
+from pytorch_pretrained_bert.modeling_xlnet import XLNetConfig, XLNetRunConfig, XLNetModel, load_tf_weights_in_xlnet
+
+def convert_xlnet_checkpoint_to_pytorch(tf_checkpoint_path, bert_config_file, pytorch_dump_path):
+    # Initialise PyTorch model
+    config = XLNetConfig.from_json_file(bert_config_file)
+    print("Building PyTorch model from configuration: {}".format(str(config)))
+    model = XLNetModel(config)
+
+    # Load weights from tf checkpoint
+    load_tf_weights_in_xlnet(model, tf_checkpoint_path)
+
+    # Save pytorch-model
+    print("Save PyTorch model to {}".format(pytorch_dump_path))
+    torch.save(model.state_dict(), pytorch_dump_path)
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser()
+    ## Required parameters
+    parser.add_argument("--tf_checkpoint_path",
+                        default = None,
+                        type = str,
+                        required = True,
+                        help = "Path the TensorFlow checkpoint path.")
+    parser.add_argument("--xlnet_config_file",
+                        default = None,
+                        type = str,
+                        required = True,
+                        help = "The config json file corresponding to the pre-trained XLNet model. \n"
+                            "This specifies the model architecture.")
+    parser.add_argument("--pytorch_dump_path",
+                        default = None,
+                        type = str,
+                        required = True,
+                        help = "Path to the output PyTorch model.")
+    args = parser.parse_args()
+    convert_xlnet_checkpoint_to_pytorch(args.tf_checkpoint_path,
+                                     args.xlnet_config_file,
+                                     args.pytorch_dump_path)

pytorch_pretrained_bert/modeling.py

@@ -718,7 +718,7 @@ class BertPreTrainedModel(nn.Module):
             state_dict = torch.load(resolved_archive_file, map_location='cpu')
         if from_tf:
             # Directly load from a TensorFlow checkpoint
-            return load_tf_weights_in_bert(model, weights_path)
+            return load_tf_weights_in_bert(model, resolved_archive_file)
         # Load from a PyTorch state_dict
         old_keys = []
         new_keys = []

pytorch_pretrained_bert/modeling_transfo_xl.py

@@ -236,7 +236,7 @@ class TransfoXLConfig(object):
             dropout: The dropout probabilitiy for all fully connected
                 layers in the embeddings, encoder, and pooler.
             dropatt: The dropout ratio for the attention probabilities.
-            untie_r: untie relative position biases           
+            untie_r: untie relative position biases
             embd_pdrop: The dropout ratio for the embeddings.
             init: parameter initializer to use
             init_range: parameters initialized by U(-init_range, init_range).

pytorch_pretrained_bert/modeling_xlnet.py

+# coding=utf-8
+# Copyright 2018 Google AI, Google Brain and Carnegie Mellon University Authors and the HuggingFace Inc. team.
+# Copyright (c) 2018, NVIDIA CORPORATION.  All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+""" PyTorch XLNet model.
+"""
+from __future__ import (absolute_import, division, print_function,
+                        unicode_literals)
+from __future__ import absolute_import, division, print_function, unicode_literals
+
+import copy
+import json
+import logging
+import math
+import os
+import sys
+from io import open
+
+import torch
+from torch import nn
+from torch.nn import CrossEntropyLoss
+
+from .file_utils import cached_path, WEIGHTS_NAME, CONFIG_NAME
+
+logger = logging.getLogger(__name__)
+
+PRETRAINED_MODEL_ARCHIVE_MAP = {
+    'xlnet-large-cased': "https://s3.amazonaws.com/models.huggingface.co/bert/xlnet-large-cased-pytorch_model.bin",
+}
+PRETRAINED_CONFIG_ARCHIVE_MAP = {
+    'xlnet-large-cased': "https://s3.amazonaws.com/models.huggingface.co/bert/xlnet-large-cased-config.json",
+}
+XLNET_CONFIG_NAME = 'xlnet_config.json'
+TF_WEIGHTS_NAME = 'model.ckpt'
+
+def load_tf_weights_in_xlnet(model, tf_checkpoint_path):
+    """ Load tf checkpoints in a pytorch model
+    """
+    try:
+        import re
+        import numpy as np
+        import tensorflow as tf
+    except ImportError:
+        print("Loading a TensorFlow models in PyTorch, requires TensorFlow to be installed. Please see "
+            "https://www.tensorflow.org/install/ for installation instructions.")
+        raise
+    tf_path = os.path.abspath(tf_checkpoint_path)
+    print("Converting TensorFlow checkpoint from {}".format(tf_path))
+    # Load weights from TF model
+    init_vars = tf.train.list_variables(tf_path)
+    names = []
+    arrays = []
+    for name, shape in init_vars:
+        print("Loading TF weight {} with shape {}".format(name, shape))
+        array = tf.train.load_variable(tf_path, name)
+        names.append(name)
+        arrays.append(array)
+
+    for name, array in zip(names, arrays):
+        name = name.split('/')
+        # adam_v and adam_m are variables used in AdamWeightDecayOptimizer to calculated m and v
+        # which are not required for using pretrained model
+        if any(n in ["adam_v", "adam_m", "global_step"] for n in name):
+            print("Skipping {}".format("/".join(name)))
+            continue
+        pointer = model
+        for m_name in name:
+            if re.fullmatch(r'[A-Za-z]+_\d+', m_name):
+                l = re.split(r'_(\d+)', m_name)
+            else:
+                l = [m_name]
+            if l[0] == 'kernel' or l[0] == 'gamma':
+                pointer = getattr(pointer, 'weight')
+            elif l[0] == 'output_bias' or l[0] == 'beta':
+                pointer = getattr(pointer, 'bias')
+            elif l[0] == 'output_weights':
+                pointer = getattr(pointer, 'weight')
+            elif l[0] == 'squad':
+                pointer = getattr(pointer, 'classifier')
+            else:
+                try:
+                    pointer = getattr(pointer, l[0])
+                except AttributeError:
+                    print("Skipping {}".format("/".join(name)))
+                    continue
+            if len(l) >= 2:
+                num = int(l[1])
+                pointer = pointer[num]
+        if m_name[-11:] == '_embeddings':
+            pointer = getattr(pointer, 'weight')
+        elif m_name == 'kernel':
+            array = np.transpose(array)
+        try:
+            assert pointer.shape == array.shape
+        except AssertionError as e:
+            e.args += (pointer.shape, array.shape)
+            raise
+        print("Initialize PyTorch weight {}".format(name))
+        pointer.data = torch.from_numpy(array)
+    return model
+
+
+def gelu(x):
+    """Implementation of the gelu activation function.
+        For information: OpenAI GPT's gelu is slightly different (and gives slightly different results):
+        0.5 * x * (1 + torch.tanh(math.sqrt(2 / math.pi) * (x + 0.044715 * torch.pow(x, 3))))
+        Also see https://arxiv.org/abs/1606.08415
+    """
+    return x * 0.5 * (1.0 + torch.erf(x / math.sqrt(2.0)))
+
+
+def swish(x):
+    return x * torch.sigmoid(x)
+
+
+ACT2FN = {"gelu": gelu, "relu": torch.nn.functional.relu, "swish": swish}
+
+class XLNetBaseConfig(object):
+    @classmethod
+    def from_dict(cls, json_object):
+        """Constructs a `XLNetConfig` from a Python dictionary of parameters."""
+        config = XLNetConfig(vocab_size_or_config_json_file=-1)
+        for key, value in json_object.items():
+            config.__dict__[key] = value
+        return config
+
+    @classmethod
+    def from_json_file(cls, json_file):
+        """Constructs a `XLNetConfig` from a json file of parameters."""
+        with open(json_file, "r", encoding='utf-8') as reader:
+            text = reader.read()
+        return cls.from_dict(json.loads(text))
+
+    def __repr__(self):
+        return str(self.to_json_string())
+
+    def to_dict(self):
+        """Serializes this instance to a Python dictionary."""
+        output = copy.deepcopy(self.__dict__)
+        return output
+
+    def to_json_string(self):
+        """Serializes this instance to a JSON string."""
+        return json.dumps(self.to_dict(), indent=2, sort_keys=True) + "\n"
+
+    def to_json_file(self, json_file_path):
+        """ Save this instance to a json file."""
+        with open(json_file_path, "w", encoding='utf-8') as writer:
+            writer.write(self.to_json_string())
+
+
+class XLNetConfig(XLNetBaseConfig):
+    """Configuration class to store the configuration of a `XLNetModel`.
+    """
+    def __init__(self,
+                 vocab_size_or_config_json_file,
+                 d_model=768,
+                 n_layer=12,
+                 n_head=12,
+                 d_inner=3072,
+                 ff_activation="gelu",
+                 untie_r=True,
+
+                 max_position_embeddings=512,
+                 type_vocab_size=2,
+                 initializer_range=0.02,
+                 layer_norm_eps=1e-12):
+        """Constructs XLNetConfig.
+
+        Args:
+            vocab_size_or_config_json_file: Vocabulary size of `inputs_ids` in `XLNetModel`.
+            d_model: Size of the encoder layers and the pooler layer.
+            n_layer: Number of hidden layers in the Transformer encoder.
+            n_head: Number of attention heads for each attention layer in
+                the Transformer encoder.
+            d_inner: The size of the "intermediate" (i.e., feed-forward)
+                layer in the Transformer encoder.
+            ff_activation: The non-linear activation function (function or string) in the
+                encoder and pooler. If string, "gelu", "relu" and "swish" are supported.
+            untie_r: untie relative position biases
+
+            dropout: The dropout probabilitiy for all fully connected
+                layers in the embeddings, encoder, and pooler.
+            dropatt: The dropout ratio for the attention
+                probabilities.
+            max_position_embeddings: The maximum sequence length that this model might
+                ever be used with. Typically set this to something large just in case
+                (e.g., 512 or 1024 or 2048).
+            type_vocab_size: The vocabulary size of the `token_type_ids` passed into
+                `XLNetModel`.
+            initializer_range: The sttdev of the truncated_normal_initializer for
+                initializing all weight matrices.
+            layer_norm_eps: The epsilon used by LayerNorm.
+        """
+        if isinstance(vocab_size_or_config_json_file, str) or (sys.version_info[0] == 2
+                        and isinstance(vocab_size_or_config_json_file, unicode)):
+            with open(vocab_size_or_config_json_file, "r", encoding='utf-8') as reader:
+                json_config = json.loads(reader.read())
+            for key, value in json_config.items():
+                self.__dict__[key] = value
+        elif isinstance(vocab_size_or_config_json_file, int):
+            self.vocab_size = vocab_size_or_config_json_file
+            self.d_model = d_model
+            self.n_layer = n_layer
+            self.n_head = n_head
+            self.ff_activation = ff_activation
+            self.d_inner = d_inner
+            self.untie_r = untie_r
+            self.max_position_embeddings = max_position_embeddings
+            self.type_vocab_size = type_vocab_size
+            self.initializer_range = initializer_range
+            self.layer_norm_eps = layer_norm_eps
+        else:
+            raise ValueError("First argument must be either a vocabulary size (int)"
+                             "or the path to a pretrained model config file (str)")
+
+
+class XLNetRunConfig(XLNetBaseConfig):
+    """XLNetRunConfig contains hyperparameters that could be different
+    between pretraining and finetuning.
+    These hyperparameters can also be changed from run to run.
+    We store them separately from XLNetConfig for flexibility.
+    """
+    def __init__(self, 
+                 dropout,
+                 dropatt,
+                 init="normal",
+                 init_range=0.1,
+                 init_std=0.02,
+                 mem_len=None,
+                 reuse_len=None,
+                 bi_data=False,
+                 clamp_len=-1,
+                 same_length=False):
+        """
+        Args:
+        dropout: float, dropout rate.
+        dropatt: float, dropout rate on attention probabilities.
+        init: str, the initialization scheme, either "normal" or "uniform".
+        init_range: float, initialize the parameters with a uniform distribution
+            in [-init_range, init_range]. Only effective when init="uniform".
+        init_std: float, initialize the parameters with a normal distribution
+            with mean 0 and stddev init_std. Only effective when init="normal".
+        mem_len: int, the number of tokens to cache.
+        reuse_len: int, the number of tokens in the currect batch to be cached
+            and reused in the future.
+        bi_data: bool, whether to use bidirectional input pipeline.
+            Usually set to True during pretraining and False during finetuning.
+        clamp_len: int, clamp all relative distances larger than clamp_len.
+            -1 means no clamping.
+        same_length: bool, whether to use the same attention length for each token.
+        """
+
+        self.init = init
+        self.init_range = init_range
+        self.init_std = init_std
+        self.dropout = dropout
+        self.dropatt = dropatt
+        self.mem_len = mem_len
+        self.reuse_len = reuse_len
+        self.bi_data = bi_data
+        self.clamp_len = clamp_len
+        self.same_length = same_length
+
+try:
+    from apex.normalization.fused_layer_norm import FusedLayerNorm as XLNetLayerNorm
+except ImportError:
+    logger.info("Better speed can be achieved with apex installed from https://www.github.com/nvidia/apex .")
+    class XLNetLayerNorm(nn.Module):
+        def __init__(self, hidden_size, eps=1e-12):
+            """Construct a layernorm module in the TF style (epsilon inside the square root).
+            """
+            super(XLNetLayerNorm, self).__init__()
+            self.weight = nn.Parameter(torch.ones(hidden_size))
+            self.bias = nn.Parameter(torch.zeros(hidden_size))
+            self.variance_epsilon = eps
+
+        def forward(self, x):
+            u = x.mean(-1, keepdim=True)
+            s = (x - u).pow(2).mean(-1, keepdim=True)
+            x = (x - u) / torch.sqrt(s + self.variance_epsilon)
+            return self.weight * x + self.bias
+
+class XLNetPreTrainedModel(nn.Module):
+    """ An abstract class to handle weights initialization and
+        a simple interface for dowloading and loading pretrained models.
+    """
+    def __init__(self, config, *inputs, **kwargs):
+        super(XLNetPreTrainedModel, self).__init__()
+        if not isinstance(config, XLNetConfig):
+            raise ValueError(
+                "Parameter config in `{}(config)` should be an instance of class `XLNetConfig`. "
+                "To create a model from a Google pretrained model use "
+                "`model = {}.from_pretrained(PRETRAINED_MODEL_NAME)`".format(
+                    self.__class__.__name__, self.__class__.__name__
+                ))
+        self.config = config
+
+    def init_xlnet_weights(self, module):
+        """ Initialize the weights.
+        """
+        if isinstance(module, (nn.Linear, nn.Embedding)):
+            # Slightly different from the TF version which uses truncated_normal for initialization
+            # cf https://github.com/pytorch/pytorch/pull/5617
+            module.weight.data.normal_(mean=0.0, std=self.config.initializer_range)
+        elif isinstance(module, XLNetLayerNorm):
+            module.bias.data.zero_()
+            module.weight.data.fill_(1.0)
+        if isinstance(module, nn.Linear) and module.bias is not None:
+            module.bias.data.zero_()
+
+    @classmethod
+    def from_pretrained(cls, pretrained_model_name_or_path, *inputs, **kwargs):
+        """
+        Instantiate a XLNetPreTrainedModel from a pre-trained model file or a pytorch state dict.
+        Download and cache the pre-trained model file if needed.
+
+        Params:
+            pretrained_model_name_or_path: either:
+                - a str with the name of a pre-trained model to load selected in the list of:
+                    . `xlnet-large-cased`
+                - a path or url to a pretrained model archive containing:
+                    . `xlnet_config.json` a configuration file for the model
+                    . `pytorch_model.bin` a PyTorch dump of a XLNetForPreTraining instance
+                - a path or url to a pretrained model archive containing:
+                    . `xlnet_config.json` a configuration file for the model
+                    . `model.chkpt` a TensorFlow checkpoint
+            from_tf: should we load the weights from a locally saved TensorFlow checkpoint
+            cache_dir: an optional path to a folder in which the pre-trained models will be cached.
+            state_dict: an optional state dictionnary (collections.OrderedDict object) to use instead of Google pre-trained models
+            *inputs, **kwargs: additional input for the specific XLNet class
+                (ex: num_labels for XLNetForSequenceClassification)
+        """
+        state_dict = kwargs.get('state_dict', None)
+        kwargs.pop('state_dict', None)
+        cache_dir = kwargs.get('cache_dir', None)
+        kwargs.pop('cache_dir', None)
+        from_tf = kwargs.get('from_tf', False)
+        kwargs.pop('from_tf', None)
+
+        if pretrained_model_name_or_path in PRETRAINED_MODEL_ARCHIVE_MAP:
+            archive_file = PRETRAINED_MODEL_ARCHIVE_MAP[pretrained_model_name_or_path]
+            config_file = PRETRAINED_CONFIG_ARCHIVE_MAP[pretrained_model_name_or_path]
+        else:
+            if from_tf:
+                # Directly load from a TensorFlow checkpoint
+                archive_file = os.path.join(pretrained_model_name_or_path, TF_WEIGHTS_NAME)
+                config_file = os.path.join(pretrained_model_name_or_path, XLNET_CONFIG_NAME)
+            else:
+                archive_file = os.path.join(pretrained_model_name_or_path, WEIGHTS_NAME)
+                config_file = os.path.join(pretrained_model_name_or_path, CONFIG_NAME)
+        # redirect to the cache, if necessary
+        try:
+            resolved_archive_file = cached_path(archive_file, cache_dir=cache_dir)
+        except EnvironmentError:
+            if pretrained_model_name_or_path in PRETRAINED_MODEL_ARCHIVE_MAP:
+                logger.error(
+                    "Couldn't reach server at '{}' to download pretrained weights.".format(
+                        archive_file))
+            else:
+                logger.error(
+                    "Model name '{}' was not found in model name list ({}). "
+                    "We assumed '{}' was a path or url but couldn't find any file "
+                    "associated to this path or url.".format(
+                        pretrained_model_name_or_path,
+                        ', '.join(PRETRAINED_MODEL_ARCHIVE_MAP.keys()),
+                        archive_file))
+            return None
+        try:
+            resolved_config_file = cached_path(config_file, cache_dir=cache_dir)
+        except EnvironmentError:
+            if pretrained_model_name_or_path in PRETRAINED_CONFIG_ARCHIVE_MAP:
+                logger.error(
+                    "Couldn't reach server at '{}' to download pretrained model configuration file.".format(
+                        config_file))
+            else:
+                logger.error(
+                    "Model name '{}' was not found in model name list ({}). "
+                    "We assumed '{}' was a path or url but couldn't find any file "
+                    "associated to this path or url.".format(
+                        pretrained_model_name_or_path,
+                        ', '.join(PRETRAINED_CONFIG_ARCHIVE_MAP.keys()),
+                        config_file))
+            return None
+        if resolved_archive_file == archive_file and resolved_config_file == config_file:
+            logger.info("loading weights file {}".format(archive_file))
+            logger.info("loading configuration file {}".format(config_file))
+        else:
+            logger.info("loading weights file {} from cache at {}".format(
+                archive_file, resolved_archive_file))
+            logger.info("loading configuration file {} from cache at {}".format(
+                config_file, resolved_config_file))
+        # Load config
+        config = XLNetConfig.from_json_file(resolved_config_file)
+        logger.info("Model config {}".format(config))
+        # Instantiate model.
+        model = cls(config, *inputs, **kwargs)
+        if state_dict is None and not from_tf:
+            state_dict = torch.load(resolved_archive_file, map_location='cpu')
+        if from_tf:
+            # Directly load from a TensorFlow checkpoint
+            return load_tf_weights_in_xlnet(model, resolved_archive_file)
+        # Load from a PyTorch state_dict
+        missing_keys = []
+        unexpected_keys = []
+        error_msgs = []
+        # copy state_dict so _load_from_state_dict can modify it
+        metadata = getattr(state_dict, '_metadata', None)
+        state_dict = state_dict.copy()
+        if metadata is not None:
+            state_dict._metadata = metadata
+
+        def load(module, prefix=''):
+            local_metadata = {} if metadata is None else metadata.get(prefix[:-1], {})
+            module._load_from_state_dict(
+                state_dict, prefix, local_metadata, True, missing_keys, unexpected_keys, error_msgs)
+            for name, child in module._modules.items():
+                if child is not None:
+                    load(child, prefix + name + '.')
+        start_prefix = ''
+        if not hasattr(model, 'xlnet') and any(s.startswith('xlnet.') for s in state_dict.keys()):
+            start_prefix = 'xlnet.'
+        load(model, prefix=start_prefix)
+        if len(missing_keys) > 0:
+            logger.info("Weights of {} not initialized from pretrained model: {}".format(
+                model.__class__.__name__, missing_keys))
+        if len(unexpected_keys) > 0:
+            logger.info("Weights from pretrained model not used in {}: {}".format(
+                model.__class__.__name__, unexpected_keys))
+        if len(error_msgs) > 0:
+            raise RuntimeError('Error(s) in loading state_dict for {}:\n\t{}'.format(
+                               model.__class__.__name__, "\n\t".join(error_msgs)))
+        return model
+
+
+class XLNetModel(XLNetPreTrainedModel):
+    """XLNet model ("XLNet: Generalized Autoregressive Pretraining for Language Understanding").
+
+    Params:
+        `config`: a XLNetConfig class instance with the configuration to build a new model
+        `output_attentions`: If True, also output attentions weights computed by the model at each layer. Default: False
+        `keep_multihead_output`: If True, saves output of the multi-head attention module with its gradient.
+            This can be used to compute head importance metrics. Default: False
+
+    Inputs:
+        `input_ids`: a torch.LongTensor of shape [batch_size, sequence_length]
+            with the word token indices in the vocabulary(see the tokens preprocessing logic in the scripts
+            `extract_features.py`, `run_classifier.py` and `run_squad.py`)
+        `token_type_ids`: an optional torch.LongTensor of shape [batch_size, sequence_length] with the token
+            types indices selected in [0, 1]. Type 0 corresponds to a `sentence A` and type 1 corresponds to
+            a `sentence B` token (see XLNet paper for more details).
+        `attention_mask`: an optional torch.LongTensor of shape [batch_size, sequence_length] with indices
+            selected in [0, 1]. It's a mask to be used if the input sequence length is smaller than the max
+            input sequence length in the current batch. It's the mask that we typically use for attention when
+            a batch has varying length sentences.
+        `output_all_encoded_layers`: boolean which controls the content of the `encoded_layers` output as described below. Default: `True`.
+        `head_mask`: an optional torch.Tensor of shape [num_heads] or [num_layers, num_heads] with indices between 0 and 1.
+            It's a mask to be used to nullify some heads of the transformer. 1.0 => head is fully masked, 0.0 => head is not masked.
+
+
+    Outputs: Tuple of (encoded_layers, pooled_output)
+        `encoded_layers`: controled by `output_all_encoded_layers` argument:
+            - `output_all_encoded_layers=True`: outputs a list of the full sequences of encoded-hidden-states at the end
+                of each attention block (i.e. 12 full sequences for XLNet-base, 24 for XLNet-large), each
+                encoded-hidden-state is a torch.FloatTensor of size [batch_size, sequence_length, hidden_size],
+            - `output_all_encoded_layers=False`: outputs only the full sequence of hidden-states corresponding
+                to the last attention block of shape [batch_size, sequence_length, hidden_size],
+        `pooled_output`: a torch.FloatTensor of size [batch_size, hidden_size] which is the output of a
+            classifier pretrained on top of the hidden state associated to the first character of the
+            input (`CLS`) to train on the Next-Sentence task (see XLNet's paper).
+
+    Example usage:
+    ```python
+    # Already been converted into WordPiece token ids
+    input_ids = torch.LongTensor([[31, 51, 99], [15, 5, 0]])
+    input_mask = torch.LongTensor([[1, 1, 1], [1, 1, 0]])
+    token_type_ids = torch.LongTensor([[0, 0, 1], [0, 1, 0]])
+
+    config = modeling.XLNetConfig(vocab_size_or_config_json_file=32000, hidden_size=768,
+        num_hidden_layers=12, num_attention_heads=12, intermediate_size=3072)
+
+    model = modeling.XLNetModel(config=config)
+    all_encoder_layers, pooled_output = model(input_ids, token_type_ids, input_mask)
+    ```
+    """
+    def __init__(self, config, output_attentions=False, keep_multihead_output=False):
+        super(XLNetModel, self).__init__(config)
+        self.output_attentions = output_attentions
+        self.apply(self.init_xlnet_weights)
+
+    def prune_heads(self, heads_to_prune):
+        """ Prunes heads of the model.
+            heads_to_prune: dict of {layer_num: list of heads to prune in this layer}
+        """
+        for layer, heads in heads_to_prune.items():
+            self.encoder.layer[layer].attention.prune_heads(heads)
+
+    def get_multihead_outputs(self):
+        """ Gather all multi-head outputs.
+            Return: list (layers) of multihead module outputs with gradients
+        """
+        return [layer.attention.self.multihead_output for layer in self.encoder.layer]
+
+    def forward(self, input_ids, token_type_ids=None, attention_mask=None, output_all_encoded_layers=True, head_mask=None):
+        if attention_mask is None:
+            attention_mask = torch.ones_like(input_ids)
+        if token_type_ids is None:
+            token_type_ids = torch.zeros_like(input_ids)
+
+        # We create a 3D attention mask from a 2D tensor mask.
+        # Sizes are [batch_size, 1, 1, to_seq_length]
+        # So we can broadcast to [batch_size, num_heads, from_seq_length, to_seq_length]
+        # this attention mask is more simple than the triangular masking of causal attention
+        # used in OpenAI GPT, we just need to prepare the broadcast dimension here.
+        extended_attention_mask = attention_mask.unsqueeze(1).unsqueeze(2)
+
+        # Since attention_mask is 1.0 for positions we want to attend and 0.0 for
+        # masked positions, this operation will create a tensor which is 0.0 for
+        # positions we want to attend and -10000.0 for masked positions.
+        # Since we are adding it to the raw scores before the softmax, this is
+        # effectively the same as removing these entirely.
+        extended_attention_mask = extended_attention_mask.to(dtype=next(self.parameters()).dtype) # fp16 compatibility
+        extended_attention_mask = (1.0 - extended_attention_mask) * -10000.0
+
+        # Prepare head mask if needed
+        # 1.0 in head_mask indicate we keep the head
+        # attention_probs has shape bsz x n_heads x N x N
+        # input head_mask has shape [num_heads] or [num_hidden_layers x num_heads]
+        # and head_mask is converted to shape [num_hidden_layers x batch x num_heads x seq_length x seq_length]
+        if head_mask is not None:
+            if head_mask.dim() == 1:
+                head_mask = head_mask.unsqueeze(0).unsqueeze(0).unsqueeze(-1).unsqueeze(-1)
+                head_mask = head_mask.expand_as(self.config.num_hidden_layers, -1, -1, -1, -1)
+            elif head_mask.dim() == 2:
+                head_mask = head_mask.unsqueeze(1).unsqueeze(-1).unsqueeze(-1)  # We can specify head_mask for each layer
+            head_mask = head_mask.to(dtype=next(self.parameters()).dtype) # switch to fload if need + fp16 compatibility
+        else:
+            head_mask = [None] * self.config.num_hidden_layers
+
+        embedding_output = self.embeddings(input_ids, token_type_ids)
+        encoded_layers = self.encoder(embedding_output,
+                                      extended_attention_mask,
+                                      output_all_encoded_layers=output_all_encoded_layers,
+                                      head_mask=head_mask)
+        if self.output_attentions:
+            all_attentions, encoded_layers = encoded_layers
+        sequence_output = encoded_layers[-1]
+        pooled_output = self.pooler(sequence_output)
+        if not output_all_encoded_layers:
+            encoded_layers = encoded_layers[-1]
+        if self.output_attentions:
+            return all_attentions, encoded_layers, pooled_output
+        return encoded_layers, pooled_output
+    
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