modeling_openai.py 37.3 KB
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# coding=utf-8
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# Copyright 2018 The OpenAI Team Authors and HuggingFace Inc. team.
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# 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 OpenAI GPT model."""

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from __future__ import absolute_import, division, print_function, unicode_literals

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import collections
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import copy
import json
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import logging
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import math
import os
import shutil
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import tarfile
import tempfile
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import sys
from io import open
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import torch
import torch.nn as nn
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from torch.nn import CrossEntropyLoss
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from torch.nn.parameter import Parameter

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from .file_utils import cached_path, CONFIG_NAME, WEIGHTS_NAME
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from .modeling import BertLayerNorm as LayerNorm
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logger = logging.getLogger(__name__)

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PRETRAINED_MODEL_ARCHIVE_MAP = {"openai-gpt": "https://s3.amazonaws.com/models.huggingface.co/bert/openai-gpt-pytorch_model.bin"}
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PRETRAINED_CONFIG_ARCHIVE_MAP = {"openai-gpt": "https://s3.amazonaws.com/models.huggingface.co/bert/openai-gpt-config.json"}
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def load_tf_weights_in_openai_gpt(model, openai_checkpoint_folder_path):
    """ Load tf pre-trained weights in a pytorch model (from NumPy arrays here)
    """
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    import re
    import numpy as np
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    print("Loading weights...")
    names = json.load(open(openai_checkpoint_folder_path + '/parameters_names.json', "r", encoding='utf-8'))
    shapes = json.load(open(openai_checkpoint_folder_path + '/params_shapes.json', "r", encoding='utf-8'))
    offsets = np.cumsum([np.prod(shape) for shape in shapes])
    init_params = [np.load(openai_checkpoint_folder_path + '/params_{}.npy'.format(n)) for n in range(10)]
    init_params = np.split(np.concatenate(init_params, 0), offsets)[:-1]
    init_params = [param.reshape(shape) for param, shape in zip(init_params, shapes)]

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    # This was used when we had a single embedding matrix for positions and tokens
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    # init_params[0] = np.concatenate([init_params[1], init_params[0]], 0)
    # del init_params[1]
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    init_params = [arr.squeeze() for arr in init_params]

    try:
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        assert model.tokens_embed.weight.shape == init_params[1].shape
        assert model.positions_embed.weight.shape == init_params[0].shape
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    except AssertionError as e:
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        e.args += (model.tokens_embed.weight.shape, init_params[1].shape)
        e.args += (model.positions_embed.weight.shape, init_params[0].shape)
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        raise

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    model.tokens_embed.weight.data = torch.from_numpy(init_params[1])
    model.positions_embed.weight.data = torch.from_numpy(init_params[0])
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    names.pop(0)
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    # Pop position and token embedding arrays
    init_params.pop(0)
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    init_params.pop(0)

    for name, array in zip(names, init_params): # names[1:n_transfer], init_params[1:n_transfer]):
        name = name[6:]  # skip "model/"
        assert name[-2:] == ":0"
        name = name[:-2]
        name = name.split('/')
        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] == 'g':
                pointer = getattr(pointer, 'weight')
            elif l[0] == 'b':
                pointer = getattr(pointer, 'bias')
            elif l[0] == 'w':
                pointer = getattr(pointer, 'weight')
            else:
                pointer = getattr(pointer, l[0])
            if len(l) >= 2:
                num = int(l[1])
                pointer = pointer[num]
        try:
            assert pointer.shape == array.shape
        except AssertionError as e:
            e.args += (pointer.shape, array.shape)
            raise
        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

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def gelu(x):
    return 0.5 * x * (1 + torch.tanh(math.sqrt(2 / math.pi) * (x + 0.044715 * torch.pow(x, 3))))


def swish(x):
    return x * torch.sigmoid(x)


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ACT_FNS = {"relu": nn.ReLU, "swish": swish, "gelu": gelu}

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class OpenAIGPTConfig(object):
    """Configuration class to store the configuration of a `OpenAIGPTModel`.
    """
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    def __init__(
        self,
        vocab_size_or_config_json_file=40478,
        n_special=0,
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        n_positions=512,
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        n_ctx=512,
        n_embd=768,
        n_layer=12,
        n_head=12,
        afn="gelu",
        resid_pdrop=0.1,
        embd_pdrop=0.1,
        attn_pdrop=0.1,
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        layer_norm_epsilon=1e-5,
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        initializer_range=0.02,
    ):
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        """Constructs OpenAIGPTConfig.

        Args:
            vocab_size_or_config_json_file: Vocabulary size of `inputs_ids` in `OpenAIGPTModel` or a configuration json file.
            n_special: The number of special tokens to learn during fine-tuning ('[SEP]', '[CLF]', ...)
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            n_positions: Number of positional embeddings.
            n_ctx: Size of the causal mask (usually same as n_positions).
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            n_embd: Dimensionality of the embeddings and hidden states.
            n_layer: Number of hidden layers in the Transformer encoder.
            n_head: Number of attention heads for each attention layer in
                the Transformer encoder.
            afn: The non-linear activation function (function or string) in the
                encoder and pooler. If string, "gelu", "relu" and "swish" are supported.
            resid_pdrop: The dropout probabilitiy for all fully connected
                layers in the embeddings, encoder, and pooler.
            attn_pdrop: The dropout ratio for the attention
                probabilities.
            embd_pdrop: The dropout ratio for the embeddings.
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            layer_norm_epsilon: epsilon to use in the layer norm layers
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            initializer_range: The sttdev of the truncated_normal_initializer for
                initializing all weight matrices.
        """
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        if isinstance(vocab_size_or_config_json_file, str) or (sys.version_info[0] == 2
                        and isinstance(vocab_size_or_config_json_file, unicode)):
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            with open(vocab_size_or_config_json_file, "r", encoding="utf-8") as reader:
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                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.n_special = n_special
            self.n_ctx = n_ctx
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            self.n_positions = n_positions
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            self.n_embd = n_embd
            self.n_layer = n_layer
            self.n_head = n_head
            self.afn = afn
            self.resid_pdrop = resid_pdrop
            self.embd_pdrop = embd_pdrop
            self.attn_pdrop = attn_pdrop
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            self.layer_norm_epsilon = layer_norm_epsilon
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            self.initializer_range = initializer_range
        else:
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            raise ValueError(
                "First argument must be either a vocabulary size (int)"
                "or the path to a pretrained model config file (str)"
            )
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    @property
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    def total_tokens_embeddings(self):
        return self.vocab_size + self.n_special
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    @classmethod
    def from_dict(cls, json_object):
        """Constructs a `OpenAIGPTConfig` from a Python dictionary of parameters."""
        config = OpenAIGPTConfig(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 `OpenAIGPTConfig` from a json file of parameters."""
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        with open(json_file, "r", encoding="utf-8") as reader:
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            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"

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    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())

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class Conv1D(nn.Module):
    def __init__(self, nf, rf, nx):
        super(Conv1D, self).__init__()
        self.rf = rf
        self.nf = nf
        if rf == 1:  # faster 1x1 conv
            w = torch.empty(nx, nf)
            nn.init.normal_(w, std=0.02)
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            self.weight = Parameter(w)
            self.bias = Parameter(torch.zeros(nf))
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        else:  # was used to train LM
            raise NotImplementedError

    def forward(self, x):
        if self.rf == 1:
            size_out = x.size()[:-1] + (self.nf,)
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            x = torch.addmm(self.bias, x.view(-1, x.size(-1)), self.weight)
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            x = x.view(*size_out)
        else:
            raise NotImplementedError
        return x


class Attention(nn.Module):
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    def __init__(self, nx, n_ctx, config, scale=False):
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        super(Attention, self).__init__()
        n_state = nx  # in Attention: n_state=768 (nx=n_embd)
        # [switch nx => n_state from Block to Attention to keep identical to TF implem]
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        assert n_state % config.n_head == 0
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        self.register_buffer("bias", torch.tril(torch.ones(n_ctx, n_ctx)).view(1, 1, n_ctx, n_ctx))
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        self.n_head = config.n_head
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        self.split_size = n_state
        self.scale = scale
        self.c_attn = Conv1D(n_state * 3, 1, nx)
        self.c_proj = Conv1D(n_state, 1, nx)
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        self.attn_dropout = nn.Dropout(config.attn_pdrop)
        self.resid_dropout = nn.Dropout(config.resid_pdrop)
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    def _attn(self, q, k, v):
        w = torch.matmul(q, k)
        if self.scale:
            w = w / math.sqrt(v.size(-1))
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        # w = w * self.bias + -1e9 * (1 - self.bias)  # TF implem method: mask_attn_weights
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        # XD: self.b may be larger than w, so we need to crop it
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        b = self.bias[:, :, : w.size(-2), : w.size(-1)]
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        w = w * b + -1e9 * (1 - b)

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        w = nn.Softmax(dim=-1)(w)
        w = self.attn_dropout(w)
        return torch.matmul(w, v)

    def merge_heads(self, x):
        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)  # in Tensorflow implem: fct merge_states

    def split_heads(self, x, k=False):
        new_x_shape = x.size()[:-1] + (self.n_head, x.size(-1) // self.n_head)
        x = x.view(*new_x_shape)  # in Tensorflow implem: fct split_states
        if k:
            return x.permute(0, 2, 3, 1)
        else:
            return x.permute(0, 2, 1, 3)

    def forward(self, x):
        x = self.c_attn(x)
        query, key, value = x.split(self.split_size, dim=2)
        query = self.split_heads(query)
        key = self.split_heads(key, k=True)
        value = self.split_heads(value)
        a = self._attn(query, key, value)
        a = self.merge_heads(a)
        a = self.c_proj(a)
        a = self.resid_dropout(a)
        return a


class MLP(nn.Module):
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    def __init__(self, n_state, config):  # in MLP: n_state=3072 (4 * n_embd)
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        super(MLP, self).__init__()
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        nx = config.n_embd
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        self.c_fc = Conv1D(n_state, 1, nx)
        self.c_proj = Conv1D(nx, 1, n_state)
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        self.act = ACT_FNS[config.afn]
        self.dropout = nn.Dropout(config.resid_pdrop)
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    def forward(self, x):
        h = self.act(self.c_fc(x))
        h2 = self.c_proj(h)
        return self.dropout(h2)


class Block(nn.Module):
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    def __init__(self, n_ctx, config, scale=False):
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        super(Block, self).__init__()
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        nx = config.n_embd
        self.attn = Attention(nx, n_ctx, config, scale)
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        self.ln_1 = LayerNorm(nx, eps=config.layer_norm_epsilon)
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        self.mlp = MLP(4 * nx, config)
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        self.ln_2 = LayerNorm(nx, eps=config.layer_norm_epsilon)
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    def forward(self, x):
        a = self.attn(x)
        n = self.ln_1(x + a)
        m = self.mlp(n)
        h = self.ln_2(n + m)
        return h


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class OpenAIGPTLMHead(nn.Module):
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    """ Language Model Head for the transformer """

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    def __init__(self, model_embeddings_weights, config):
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        super(OpenAIGPTLMHead, self).__init__()
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        self.n_embd = config.n_embd
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        self.set_embeddings_weights(model_embeddings_weights)

    def set_embeddings_weights(self, model_embeddings_weights):
        embed_shape = model_embeddings_weights.shape
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        self.decoder = nn.Linear(embed_shape[1], embed_shape[0], bias=False)
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        self.decoder.weight = model_embeddings_weights  # Tied weights
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    def forward(self, hidden_state):
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        # Truncated Language modeling logits (we remove the last token)
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        # h_trunc = h[:, :-1].contiguous().view(-1, self.n_embd)
        lm_logits = self.decoder(hidden_state)
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        return lm_logits


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class OpenAIGPTMultipleChoiceHead(nn.Module):
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    """ Classifier Head for the transformer """

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    def __init__(self, config):
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        super(OpenAIGPTMultipleChoiceHead, self).__init__()
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        self.n_embd = config.n_embd
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        # self.multiple_choice_token = multiple_choice_token
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        self.dropout = nn.Dropout2d(config.resid_pdrop)  # To reproduce the noise_shape parameter of TF implementation
        self.linear = nn.Linear(config.n_embd, 1)
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        nn.init.normal_(self.linear.weight, std=0.02)
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        nn.init.normal_(self.linear.bias, 0)

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    def forward(self, hidden_states, mc_token_ids):
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        # Classification logits
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        # hidden_state (bsz, num_choices, seq_length, hidden_size)
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        # mc_token_ids (bsz, num_choices)
        mc_token_ids = mc_token_ids.unsqueeze(-1).unsqueeze(-1).expand(-1, -1, -1, hidden_states.size(-1))
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        # (bsz, num_choices, 1, hidden_size)
        multiple_choice_h = hidden_states.gather(2, mc_token_ids).squeeze(2)
        # (bsz, num_choices, hidden_size)
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        multiple_choice_h = self.dropout(multiple_choice_h.transpose(1, 2)).transpose(1, 2)
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        multiple_choice_logits = self.linear(multiple_choice_h).squeeze(-1)
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        # (bsz, num_choices)
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        return multiple_choice_logits


class OpenAIGPTPreTrainedModel(nn.Module):
    """ An abstract class to handle weights initialization and
        a simple interface for dowloading and loading pretrained models.
    """
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    def __init__(self, config, *inputs, **kwargs):
        super(OpenAIGPTPreTrainedModel, self).__init__()
        if not isinstance(config, OpenAIGPTConfig):
            raise ValueError(
                "Parameter config in `{}(config)` should be an instance of class `OpenAIGPTConfig`. "
                "To create a model from a pretrained model use "
                "`model = {}.from_pretrained(PRETRAINED_MODEL_NAME)`".format(
                    self.__class__.__name__, self.__class__.__name__
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                )
            )
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        self.config = config

    def init_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, LayerNorm):
            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_()
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    def set_num_special_tokens(self, num_special_tokens):
        pass

    @classmethod
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    def from_pretrained(
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        cls, pretrained_model_name_or_path, num_special_tokens=None, state_dict=None, cache_dir=None, from_tf=False, *inputs, **kwargs
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    ):
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        """
        Instantiate a OpenAIGPTPreTrainedModel from a pre-trained model file or a pytorch state dict.
        Download and cache the pre-trained model file if needed.

        Params:
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            pretrained_model_name_or_path: either:
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                - a str with the name of a pre-trained model to load selected in the list of:
                    . `openai-gpt`
                - a path or url to a pretrained model archive containing:
                    . `openai_gpt_config.json` a configuration file for the model
                    . `pytorch_model.bin` a PyTorch dump of a OpenAIGPTModel instance
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                - a path or url to a pretrained model archive containing:
                    . `bert_config.json` a configuration file for the model
                    . a series of NumPy files containing OpenAI TensorFlow trained weights
            from_tf: should we load the weights from a locally saved TensorFlow checkpoint
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            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 pre-trained models
            *inputs, **kwargs: additional input for the specific Bert class
                (ex: num_labels for BertForSequenceClassification)
        """
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        if pretrained_model_name_or_path in PRETRAINED_MODEL_ARCHIVE_MAP:
            archive_file = PRETRAINED_MODEL_ARCHIVE_MAP[pretrained_model_name_or_path]
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            config_file = PRETRAINED_CONFIG_ARCHIVE_MAP[pretrained_model_name_or_path]
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        else:
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            archive_file = os.path.join(pretrained_model_name_or_path, WEIGHTS_NAME)
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            config_file = os.path.join(pretrained_model_name_or_path, CONFIG_NAME)
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        # redirect to the cache, if necessary
        try:
            resolved_archive_file = cached_path(archive_file, cache_dir=cache_dir)
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            resolved_config_file = cached_path(config_file, cache_dir=cache_dir)
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        except EnvironmentError:
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            logger.error(
                "Model name '{}' was not found in model name list ({}). "
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                "We assumed '{}' was a path or url but couldn't find files {} and {} "
                "at this path or url.".format(
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                    pretrained_model_name_or_path, ", ".join(PRETRAINED_MODEL_ARCHIVE_MAP.keys()), pretrained_model_name_or_path,
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                    archive_file, config_file
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                )
            )
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            return None
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        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))
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        else:
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            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))
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        # Load config
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        config = OpenAIGPTConfig.from_json_file(resolved_config_file)
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        logger.info("Model config {}".format(config))
        # Instantiate model.
        model = cls(config, *inputs, **kwargs)
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        if state_dict is None and not from_tf:
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            state_dict = torch.load(resolved_archive_file, map_location='cpu' if not torch.cuda.is_available() else None)
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        if from_tf:
            # Directly load from a TensorFlow checkpoint (stored as NumPy array)
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            return load_tf_weights_in_openai_gpt(model, resolved_archive_file)
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        old_keys = []
        new_keys = []
        for key in state_dict.keys():
            new_key = None
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            if key.endswith(".g"):
                new_key = key[:-2] + ".weight"
            elif key.endswith(".b"):
                new_key = key[:-2] + ".bias"
            elif key.endswith(".w"):
                new_key = key[:-2] + ".weight"
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            if new_key:
                old_keys.append(key)
                new_keys.append(new_key)
        for old_key, new_key in zip(old_keys, new_keys):
            state_dict[new_key] = state_dict.pop(old_key)

        missing_keys = []
        unexpected_keys = []
        error_msgs = []
        # copy state_dict so _load_from_state_dict can modify it
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        metadata = getattr(state_dict, "_metadata", None)
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        state_dict = state_dict.copy()
        if metadata is not None:
            state_dict._metadata = metadata

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        def load(module, prefix=""):
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            local_metadata = {} if metadata is None else metadata.get(prefix[:-1], {})
            module._load_from_state_dict(
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                state_dict, prefix, local_metadata, True, missing_keys, unexpected_keys, error_msgs
            )
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            for name, child in module._modules.items():
                if child is not None:
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                    load(child, prefix + name + ".")

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        start_model = model
        if hasattr(model, "transformer") and all(not s.startswith('transformer.') for s in state_dict.keys()):
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            start_model = model.transformer
        load(start_model, prefix="")

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        if len(missing_keys) > 0:
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            logger.info(
                "Weights of {} not initialized from pretrained model: {}".format(model.__class__.__name__, missing_keys)
            )
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        if len(unexpected_keys) > 0:
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            logger.info(
                "Weights from pretrained model not used in {}: {}".format(model.__class__.__name__, unexpected_keys)
            )
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        if len(error_msgs) > 0:
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            raise RuntimeError(
                "Error(s) in loading state_dict for {}:\n\t{}".format(model.__class__.__name__, "\n\t".join(error_msgs))
            )
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        # Add additional embeddings for special tokens if needed
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        # This step also make sure we are still sharing the output and input embeddings after loading weights
        model.set_num_special_tokens(num_special_tokens if num_special_tokens is not None else config.n_special)
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        return model
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class OpenAIGPTModel(OpenAIGPTPreTrainedModel):
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    """OpenAI GPT model ("Improving Language Understanding by Generative Pre-Training").

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    OpenAI GPT use a single embedding matrix to store the word and special embeddings.
    Special tokens embeddings are additional tokens that are not pre-trained: [SEP], [CLS]...
    Special tokens need to be trained during the fine-tuning if you use them.
    The number of special embeddings can be controled using the `set_num_special_tokens(num_special_tokens)` function.

    The embeddings are ordered as follow in the token embeddings matrice:
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        [0,                                                         ----------------------
         ...                                                        -> word embeddings
         config.vocab_size - 1,                                     ______________________
         config.vocab_size,
         ...                                                        -> special embeddings
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         config.vocab_size + config.n_special - 1]                  ______________________
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    where total_tokens_embeddings can be obtained as config.total_tokens_embeddings and is:
        total_tokens_embeddings = config.vocab_size + config.n_special
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    You should use the associate indices to index the embeddings.

    Params:
        config: a OpenAIGPTConfig class instance with the configuration to build a new model

    Inputs:
        `input_ids`: a torch.LongTensor of shape [batch_size, sequence_length] (or more generally [d_1, ..., d_n, sequence_length]
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            were d_1 ... d_n are arbitrary dimensions) with the word BPE token indices selected in the range [0, total_tokens_embeddings[
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        `position_ids`: an optional torch.LongTensor with the same shape as input_ids
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            with the position indices (selected in the range [0, config.n_positions - 1[.
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        `token_type_ids`: an optional torch.LongTensor with the same shape as input_ids
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            You can use it to add a third type of embedding to each input token in the sequence
            (the previous two being the word and position embeddings).
            The input, position and token_type embeddings are summed inside the Transformer before the first
            self-attention block.
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    Outputs:
        `hidden_states`: the encoded-hidden-states at the top of the model
            as a torch.FloatTensor of size [batch_size, sequence_length, hidden_size]
            (or more generally [d_1, ..., d_n, hidden_size] were d_1 ... d_n are the dimension of input_ids)

    Example usage:
    ```python
    # Already been converted into BPE token ids
    input_ids = torch.LongTensor([[31, 51, 99], [15, 5, 0]])

    config = modeling_openai.OpenAIGPTConfig()

    model = modeling_openai.OpenAIGPTModel(config)
    hidden_states = model(input_ids)
    ```
    """
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    def __init__(self, config):
        super(OpenAIGPTModel, self).__init__(config)
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        num_tokens = config.vocab_size + config.n_special
        self.tokens_embed = nn.Embedding(num_tokens, config.n_embd)
        self.positions_embed = nn.Embedding(config.n_positions, config.n_embd)
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        self.drop = nn.Dropout(config.embd_pdrop)
        block = Block(config.n_ctx, config, scale=True)
        self.h = nn.ModuleList([copy.deepcopy(block) for _ in range(config.n_layer)])
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        self.apply(self.init_weights)
        # nn.init.normal_(self.embed.weight, std=0.02)

    def set_num_special_tokens(self, num_special_tokens):
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        " Update input embeddings with new embedding matrice if needed "
        if self.config.n_special == num_special_tokens:
            return
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        # Update config
        self.config.n_special = num_special_tokens
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        # Build new embeddings and initialize all new embeddings (in particular the special tokens)
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        old_embed = self.tokens_embed
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        self.tokens_embed = nn.Embedding(self.config.total_tokens_embeddings, self.config.n_embd)
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        self.init_weights(self.tokens_embed)
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        # Copy word embeddings from the previous weights
        self.tokens_embed.weight.data[:self.config.vocab_size, :] = old_embed.weight.data[:self.config.vocab_size, :]
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    def forward(self, input_ids, position_ids=None, token_type_ids=None):
        if position_ids is None:
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            # This was used when we had a single embedding matrice from position and token embeddings
            # start = self.config.vocab_size + self.config.n_special
            # end = start + input_ids.size(-1)
            # position_ids = torch.arange(start, end, dtype=torch.long, device=input_ids.device)
            position_ids = torch.arange(input_ids.size(-1), dtype=torch.long, device=input_ids.device)
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            position_ids = position_ids.unsqueeze(0).expand_as(input_ids)

        input_shape = input_ids.size()
        input_ids = input_ids.view(-1, input_ids.size(-1))
        position_ids = position_ids.view(-1, position_ids.size(-1))

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        inputs_embeds = self.tokens_embed(input_ids)
        position_embeds = self.positions_embed(position_ids)
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        if token_type_ids is not None:
            token_type_ids = token_type_ids.view(-1, token_type_ids.size(-1))
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            token_type_embeds = self.tokens_embed(token_type_ids)
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        else:
            token_type_embeds = 0
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        # Add the position information to the input embeddings
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        # h = e.sum(dim=2)
        hidden_states = inputs_embeds + position_embeds + token_type_embeds
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        for block in self.h:
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            hidden_states = block(hidden_states)
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        output_shape = input_shape + (hidden_states.size(-1),)
        return hidden_states.view(*output_shape)
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class OpenAIGPTLMHeadModel(OpenAIGPTPreTrainedModel):
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    """OpenAI GPT model with a Language Modeling head ("Improving Language Understanding by Generative Pre-Training").

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    OpenAI GPT use a single embedding matrix to store the word and special embeddings.
    Special tokens embeddings are additional tokens that are not pre-trained: [SEP], [CLS]...
    Special tokens need to be trained during the fine-tuning if you use them.
    The number of special embeddings can be controled using the `set_num_special_tokens(num_special_tokens)` function.

    The embeddings are ordered as follow in the token embeddings matrice:
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        [0,                                                         ----------------------
         ...                                                        -> word embeddings
         config.vocab_size - 1,                                     ______________________
         config.vocab_size,
         ...                                                        -> special embeddings
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         config.vocab_size + config.n_special - 1]                  ______________________
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    where total_tokens_embeddings can be obtained as config.total_tokens_embeddings and is:
        total_tokens_embeddings = config.vocab_size + config.n_special
    You should use the associate indices to index the embeddings.
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    Params:
        config: a OpenAIGPTConfig class instance with the configuration to build a new model

    Inputs:
        `input_ids`: a torch.LongTensor of shape [batch_size, sequence_length] (or more generally [d_1, ..., d_n, sequence_length]
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            were d_1 ... d_n are arbitrary dimensions) with the word BPE token indices selected in the range [0, total_tokens_embeddings[
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        `position_ids`: an optional torch.LongTensor with the same shape as input_ids
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            with the position indices (selected in the range [0, config.n_positions - 1[.
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        `token_type_ids`: an optional torch.LongTensor with the same shape as input_ids
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            You can use it to add a third type of embedding to each input token in the sequence
            (the previous two being the word and position embeddings).
            The input, position and token_type embeddings are summed inside the Transformer before the first
            self-attention block.
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        `lm_labels`: optional language modeling labels: torch.LongTensor of shape [batch_size, sequence_length]
            with indices selected in [-1, 0, ..., vocab_size]. All labels set to -1 are ignored (masked), the loss
            is only computed for the labels set in [0, ..., vocab_size]

    Outputs:
        if `lm_labels` is not `None`:
            Outputs the language modeling loss.
        else:
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            `lm_logits`: the language modeling logits as a torch.FloatTensor of size [batch_size, sequence_length, total_tokens_embeddings]
                (or more generally [d_1, ..., d_n, total_tokens_embeddings] were d_1 ... d_n are the dimension of input_ids)
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    Example usage:
    ```python
    # Already been converted into BPE token ids
    input_ids = torch.LongTensor([[31, 51, 99], [15, 5, 0]])

    config = modeling_openai.OpenAIGPTConfig()

    model = modeling_openai.OpenAIGPTLMHeadModel(config)
    lm_logits = model(input_ids)
    ```
    """
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    def __init__(self, config):
        super(OpenAIGPTLMHeadModel, self).__init__(config)
        self.transformer = OpenAIGPTModel(config)
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        self.lm_head = OpenAIGPTLMHead(self.transformer.tokens_embed.weight, config)
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        self.apply(self.init_weights)

    def set_num_special_tokens(self, num_special_tokens):
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        """ Update input and output embeddings with new embedding matrice
            Make sure we are sharing the embeddings
        """
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        self.transformer.set_num_special_tokens(num_special_tokens)
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        self.lm_head.set_embeddings_weights(self.transformer.tokens_embed.weight)
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    def forward(self, input_ids, position_ids=None, token_type_ids=None, lm_labels=None):
        hidden_states = self.transformer(input_ids, position_ids, token_type_ids)
        lm_logits = self.lm_head(hidden_states)
        if lm_labels is not None:
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            # Shift so that tokens < n predict n
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            shift_logits = lm_logits[:, :-1].contiguous()
            shift_labels = lm_labels[:, 1:].contiguous()
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            # Flatten the tokens
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            loss_fct = CrossEntropyLoss(ignore_index=-1)
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            loss = loss_fct(shift_logits.view(-1, shift_logits.size(-1)),
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                            shift_labels.view(-1))
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            return loss
        return lm_logits
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class OpenAIGPTDoubleHeadsModel(OpenAIGPTPreTrainedModel):
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    """OpenAI GPT model with a Language Modeling and a Multiple Choice head ("Improving Language Understanding by Generative Pre-Training").
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    OpenAI GPT use a single embedding matrix to store the word and special embeddings.
    Special tokens embeddings are additional tokens that are not pre-trained: [SEP], [CLS]...
    Special tokens need to be trained during the fine-tuning if you use them.
    The number of special embeddings can be controled using the `set_num_special_tokens(num_special_tokens)` function.

    The embeddings are ordered as follow in the token embeddings matrice:
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        [0,                                                         ----------------------
         ...                                                        -> word embeddings
         config.vocab_size - 1,                                     ______________________
         config.vocab_size,
         ...                                                        -> special embeddings
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         config.vocab_size + config.n_special - 1]                  ______________________
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    where total_tokens_embeddings can be obtained as config.total_tokens_embeddings and is:
        total_tokens_embeddings = config.vocab_size + config.n_special
    You should use the associate indices to index the embeddings.
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    Params:
        config: a OpenAIGPTConfig class instance with the configuration to build a new model

    Inputs:
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        `input_ids`: a torch.LongTensor of shape [batch_size, num_choices, sequence_length] with the BPE token
            indices selected in the range [0, total_tokens_embeddings[
        `mc_token_ids`: a torch.LongTensor of shape [batch_size, num_choices] with the index of the token from
            which we should take the hidden state to feed the multiple choice classifier (usually last token of the sequence)
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        `position_ids`: an optional torch.LongTensor with the same shape as input_ids
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            with the position indices (selected in the range [0, config.n_positions - 1[.
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        `token_type_ids`: an optional torch.LongTensor with the same shape as input_ids
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            You can use it to add a third type of embedding to each input token in the sequence
            (the previous two being the word and position embeddings).
            The input, position and token_type embeddings are summed inside the Transformer before the first
            self-attention block.
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        `lm_labels`: optional language modeling labels: torch.LongTensor of shape [batch_size, num_choices, sequence_length]
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            with indices selected in [-1, 0, ..., total_tokens_embeddings]. All labels set to -1 are ignored (masked), the loss
            is only computed for the labels set in [0, ..., total_tokens_embeddings]
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        `multiple_choice_labels`: optional multiple choice labels: torch.LongTensor of shape [batch_size]
            with indices selected in [0, ..., num_choices].

    Outputs:
        if `lm_labels` and `multiple_choice_labels` are not `None`:
            Outputs a tuple of losses with the language modeling loss and the multiple choice loss.
        else: a tuple with
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            `lm_logits`: the language modeling logits as a torch.FloatTensor of size [batch_size, num_choices, sequence_length, total_tokens_embeddings]
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            `multiple_choice_logits`: the multiple choice logits as a torch.FloatTensor of size [batch_size, num_choices]

    Example usage:
    ```python
    # Already been converted into BPE token ids
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    input_ids = torch.LongTensor([[[31, 51, 99], [15, 5, 0]]])  # (bsz, number of choice, seq length)
    mc_token_ids = torch.LongTensor([[2], [1]]) # (bsz, number of choice)
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    config = modeling_openai.OpenAIGPTConfig()

    model = modeling_openai.OpenAIGPTLMHeadModel(config)
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    lm_logits, multiple_choice_logits = model(input_ids, mc_token_ids)
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    ```
    """
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    def __init__(self, config):
        super(OpenAIGPTDoubleHeadsModel, self).__init__(config)
        self.transformer = OpenAIGPTModel(config)
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        self.lm_head = OpenAIGPTLMHead(self.transformer.tokens_embed.weight, config)
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        self.multiple_choice_head = OpenAIGPTMultipleChoiceHead(config)
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        self.apply(self.init_weights)
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    def set_num_special_tokens(self, num_special_tokens):
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        """ Update input and output embeddings with new embedding matrice
            Make sure we are sharing the embeddings
        """
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        self.transformer.set_num_special_tokens(num_special_tokens)
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        self.lm_head.set_embeddings_weights(self.transformer.tokens_embed.weight)
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    def forward(self, input_ids, mc_token_ids, lm_labels=None, mc_labels=None, token_type_ids=None, position_ids=None):
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        hidden_states = self.transformer(input_ids, position_ids, token_type_ids)
        lm_logits = self.lm_head(hidden_states)
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        mc_logits = self.multiple_choice_head(hidden_states, mc_token_ids)
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        losses = []
        if lm_labels is not None:
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            shift_logits = lm_logits[:, :-1].contiguous()
            shift_labels = lm_labels[:, 1:].contiguous()
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            loss_fct = CrossEntropyLoss(ignore_index=-1)
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            losses.append(loss_fct(shift_logits.view(-1,
                          shift_logits.size(-1)), shift_labels.view(-1)))
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        if mc_labels is not None:
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            loss_fct = CrossEntropyLoss()
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            losses.append(loss_fct(mc_logits.view(-1, mc_logits.size(-1)), mc_labels.view(-1)))
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        if losses:
            return losses
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        return lm_logits, mc_logits