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👾 PyTorch-Transformers

PyTorch-Transformers is a library of state-of-the-art pre-trained models for Natural Language Processing (NLP).

The library currently contains PyTorch implementations, pre-trained model weights, usage scripts and conversion utilities for the following models:

BERT (from Google) released with the paper BERT: Pre-training of Deep Bidirectional Transformers for Language Understanding by Jacob Devlin, Ming-Wei Chang, Kenton Lee and Kristina Toutanova.
GPT (from OpenAI) released with the paper Improving Language Understanding by Generative Pre-Training by Alec Radford, Karthik Narasimhan, Tim Salimans and Ilya Sutskever.
GPT-2 (from OpenAI) released with the paper Language Models are Unsupervised Multitask Learners by Alec Radford*, Jeffrey Wu*, Rewon Child, David Luan, Dario Amodei** and Ilya Sutskever**.
Transformer-XL (from Google/CMU) released with the paper Transformer-XL: Attentive Language Models Beyond a Fixed-Length Context by Zihang Dai*, Zhilin Yang*, Yiming Yang, Jaime Carbonell, Quoc V. Le, Ruslan Salakhutdinov.
XLNet (from Google/CMU) released with the paper XLNet: Generalized Autoregressive Pretraining for Language Understanding by Zhilin Yang*, Zihang Dai*, Yiming Yang, Jaime Carbonell, Ruslan Salakhutdinov, Quoc V. Le.
XLM (from Facebook) released together with the paper Cross-lingual Language Model Pretraining by Guillaume Lample and Alexis Conneau.

These implementations have been tested on several datasets (see the example scripts) and should match the performances of the original implementations (e.g. ~93 F1 on SQuAD for BERT Whole-Word-Masking, ~88 F1 on RocStories for OpenAI GPT, ~18.3 perplexity on WikiText 103 for Transformer-XL, ~0.916 Peason R coefficient on STS-B for XLNet). You can find more details on the performances in the Examples section of the documentation.

Section	Description
Installation	How to install the package
Quick tour: Usage	Tokenizers & models usage: Bert and GPT-2
Quick tour: Fine-tuning/usage scripts	Using provided scripts: GLUE, SQuAD and Text generation
Migrating from pytorch-pretrained-bert to pytorch-transformers	Migrating your code from pytorch-pretrained-bert to pytorch-transformers
Documentation	Full API documentation and more

Installation

This repo is tested on Python 2.7 and 3.5+ (examples are tested only on python 3.5+) and PyTorch 0.4.1 to 1.1.0

With pip

PyTorch-Transformers can be installed by pip as follows:

pip install pytorch-transformers

From source

Clone the repository and run:

pip install [--editable] .

Tests

A series of tests is included for the library and the example scripts. Library tests can be found in the tests folder and examples tests in the examples folder.

These tests can be run using pytest (install pytest if needed with pip install pytest).

You can run the tests from the root of the cloned repository with the commands:

python -m pytest -sv ./pytorch_transformers/tests/
python -m pytest -sv ./examples/

Quick tour: Usage

Here are two quick-start examples using Bert and GPT2 with pre-trained models.

See the documentation for the details of all the models and classes.

BERT example

First let's prepare a tokenized input from a text string using BertTokenizer

import torch
from pytorch_transformers import BertTokenizer, BertModel, BertForMaskedLM

# OPTIONAL: if you want to have more information on what's happening under the hood, activate the logger as follows
import logging
logging.basicConfig(level=logging.INFO)

# Load pre-trained model tokenizer (vocabulary)
tokenizer = BertTokenizer.from_pretrained('bert-base-uncased')

# Tokenize input
text = "[CLS] Who was Jim Henson ? [SEP] Jim Henson was a puppeteer [SEP]"
tokenized_text = tokenizer.tokenize(text)

# Mask a token that we will try to predict back with `BertForMaskedLM`
masked_index = 8
tokenized_text[masked_index] = '[MASK]'
assert tokenized_text == ['[CLS]', 'who', 'was', 'jim', 'henson', '?', '[SEP]', 'jim', '[MASK]', 'was', 'a', 'puppet', '##eer', '[SEP]']

# Convert token to vocabulary indices
indexed_tokens = tokenizer.convert_tokens_to_ids(tokenized_text)
# Define sentence A and B indices associated to 1st and 2nd sentences (see paper)
segments_ids = [0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1]

# Convert inputs to PyTorch tensors
tokens_tensor = torch.tensor([indexed_tokens])
segments_tensors = torch.tensor([segments_ids])

Let's see how we can use BertModel to encode our inputs in hidden-states:

# Load pre-trained model (weights)
model = BertModel.from_pretrained('bert-base-uncased')

# Set the model in evaluation mode to desactivate the DropOut modules
# This is IMPORTANT to have reproductible results during evaluation!
model.eval()

# If you have a GPU, put everything on cuda
tokens_tensor = tokens_tensor.to('cuda')
segments_tensors = segments_tensors.to('cuda')
model.to('cuda')

# Predict hidden states features for each layer
with torch.no_grad():
    # See the models docstrings for the detail of the inputs
    outputs = model(tokens_tensor, token_type_ids=segments_tensors)
    # PyTorch-Transformers models always output tuples.
    # See the models docstrings for the detail of all the outputs
    # In our case, the first element is the hidden state of the last layer of the Bert model
    encoded_layers = outputs[0]
# We have encoded our input sequence in a FloatTensor of shape (batch size, sequence length, model hidden dimension)
assert tuple(encoded_layers.shape) == (1, len(indexed_tokens), model.config.hidden_size)

And how to use BertForMaskedLM to predict a masked token:

# Load pre-trained model (weights)
model = BertForMaskedLM.from_pretrained('bert-base-uncased')
model.eval()

# If you have a GPU, put everything on cuda
tokens_tensor = tokens_tensor.to('cuda')
segments_tensors = segments_tensors.to('cuda')
model.to('cuda')

# Predict all tokens
with torch.no_grad():
    outputs = model(tokens_tensor, token_type_ids=segments_tensors)
    predictions = outputs[0]

# confirm we were able to predict 'henson'
predicted_index = torch.argmax(predictions[0, masked_index]).item()
predicted_token = tokenizer.convert_ids_to_tokens([predicted_index])[0]
assert predicted_token == 'henson'

OpenAI GPT-2

Here is a quick-start example using GPT2Tokenizer and GPT2LMHeadModel class with OpenAI's pre-trained model to predict the next token from a text prompt.

First let's prepare a tokenized input from our text string using GPT2Tokenizer

import torch
from pytorch_transformers import GPT2Tokenizer, GPT2LMHeadModel

# OPTIONAL: if you want to have more information on what's happening, activate the logger as follows
import logging
logging.basicConfig(level=logging.INFO)

# Load pre-trained model tokenizer (vocabulary)
tokenizer = GPT2Tokenizer.from_pretrained('gpt2')

# Encode a text inputs
text = "Who was Jim Henson ? Jim Henson was a"
indexed_tokens = tokenizer.encode(text)

# Convert indexed tokens in a PyTorch tensor
tokens_tensor = torch.tensor([indexed_tokens])

Let's see how to use GPT2LMHeadModel to generate the next token following our text:

# Load pre-trained model (weights)
model = GPT2LMHeadModel.from_pretrained('gpt2')

# Set the model in evaluation mode to desactivate the DropOut modules
# This is IMPORTANT to have reproductible results during evaluation!
model.eval()

# If you have a GPU, put everything on cuda
tokens_tensor = tokens_tensor.to('cuda')
model.to('cuda')

# Predict all tokens
with torch.no_grad():
    outputs = model(tokens_tensor)
    predictions = outputs[0]

# get the predicted next sub-word (in our case, the word 'man')
predicted_index = torch.argmax(predictions[0, -1, :]).item()
predicted_text = tokenizer.decode(indexed_tokens + [predicted_index])
assert predicted_text == 'Who was Jim Henson? Jim Henson was a man'

Examples for each model class of each model architecture (Bert, GPT, GPT-2, Transformer-XL, XLNet and XLM) can be found in the documentation.

Quick tour: Fine-tuning/usage scripts

The library comprises several example scripts with SOTA performances for NLU and NLG tasks:

run_glue.py: an example fine-tuning Bert, XLNet and XLM on nine different GLUE tasks (sequence-level classification)
run_squad.py: an example fine-tuning Bert, XLNet and XLM on the question answering dataset SQuAD 2.0 (token-level classification)
run_generation.py: an example using GPT, GPT-2, Transformer-XL and XLNet for conditional language generation
other model-specific examples (see the documentation).

Here are three quick usage examples for these scripts:

`run_glue.py`: Fine-tuning on GLUE tasks for sequence classification

The General Language Understanding Evaluation (GLUE) benchmark is a collection of nine sentence- or sentence-pair language understanding tasks for evaluating and analyzing natural language understanding systems.

Before running anyone of these GLUE tasks you should download the GLUE data by running this script and unpack it to some directory $GLUE_DIR.

export GLUE_DIR=/path/to/glue
export TASK_NAME=MRPC

python run_bert_classifier.py \
  --task_name $TASK_NAME \
  --do_train \
  --do_eval \
  --do_lower_case \
  --data_dir $GLUE_DIR/$TASK_NAME \
  --bert_model bert-base-uncased \
  --max_seq_length 128 \
  --train_batch_size 32 \
  --learning_rate 2e-5 \
  --num_train_epochs 3.0 \
  --output_dir /tmp/$TASK_NAME/

where task name can be one of CoLA, SST-2, MRPC, STS-B, QQP, MNLI, QNLI, RTE, WNLI.

The dev set results will be present within the text file 'eval_results.txt' in the specified output_dir. In case of MNLI, since there are two separate dev sets, matched and mismatched, there will be a separate output folder called '/tmp/MNLI-MM/' in addition to '/tmp/MNLI/'.

Fine-tuning XLNet model on the STS-B regression task

This example code fine-tunes XLNet on the STS-B corpus using parallel training on a server with 4 V100 GPUs. Parallel training is a simple way to use several GPU (but it is slower and less flexible than distributed training, see below).

export GLUE_DIR=/path/to/glue

python ./examples/run_glue.py \
    --model_type xlnet \
    --model_name_or_path xlnet-large-cased \
    --do_train  \
    --task_name=sts-b     \
    --data_dir=${GLUE_DIR}/STS-B  \
    --output_dir=./proc_data/sts-b-110   \
    --max_seq_length=128   \
    --per_gpu_eval_batch_size=8   \
    --per_gpu_train_batch_size=8   \
    --gradient_accumulation_steps=1 \
    --max_steps=1200  \
    --model_name=xlnet-large-cased   \
    --overwrite_output_dir   \
    --overwrite_cache \
    --warmup_steps=120

On this machine we thus have a batch size of 32, please increase gradient_accumulation_steps to reach the same batch size if you have a smaller machine. These hyper-parameters give evaluation results pearsonr of 0.918.

Fine-tuning Bert model on the MRPC classification task

This example code fine-tunes the Bert Whole Word Masking model on the Microsoft Research Paraphrase Corpus (MRPC) corpus using distributed training on 8 V100 GPUs to reach a F1 > 92.

python -m torch.distributed.launch --nproc_per_node 8 run_bert_classifier.py   \
    --model_type bert \
    --model_name_or_path bert-large-uncased-whole-word-masking \
    --task_name MRPC \
    --do_train   \
    --do_eval   \
    --do_lower_case   \
    --data_dir $GLUE_DIR/MRPC/   \
    --max_seq_length 128   \
    --per_gpu_eval_batch_size=8   \
    --per_gpu_train_batch_size=8   \
    --learning_rate 2e-5   \
    --num_train_epochs 3.0  \
    --output_dir /tmp/mrpc_output/ \
    --overwrite_output_dir   \
    --overwrite_cache \

Training with these hyper-parameters gave us the following results:

  acc = 0.8823529411764706
  acc_and_f1 = 0.901702786377709
  eval_loss = 0.3418912578906332
  f1 = 0.9210526315789473
  global_step = 174
  loss = 0.07231863956341798

`run_squad.py`: Fine-tuning on SQuAD for question-answering

This example code fine-tunes BERT on the SQuAD dataset using distributed training on 8 V100 GPUs and Bert Whole Word Masking uncased model to reach a F1 > 93 on SQuAD:

python -m torch.distributed.launch --nproc_per_node=8 run_squad.py \
    --model_type bert \
    --model_name_or_path bert-large-uncased-whole-word-masking \
    --do_train \
    --do_predict \
    --do_lower_case \
    --train_file $SQUAD_DIR/train-v1.1.json \
    --predict_file $SQUAD_DIR/dev-v1.1.json \
    --learning_rate 3e-5 \
    --num_train_epochs 2 \
    --max_seq_length 384 \
    --doc_stride 128 \
    --output_dir ../models/wwm_uncased_finetuned_squad/ \
    --per_gpu_eval_batch_size=3   \
    --per_gpu_train_batch_size=3   \

Training with these hyper-parameters gave us the following results:

python $SQUAD_DIR/evaluate-v1.1.py $SQUAD_DIR/dev-v1.1.json ../models/wwm_uncased_finetuned_squad/predictions.json
{"exact_match": 86.91579943235573, "f1": 93.1532499015869}

This is the model provided as bert-large-uncased-whole-word-masking-finetuned-squad.

`run_generation.py`: Text generation with GPT, GPT-2, Transformer-XL and XLNet

A conditional generation script is also included to generate text from a prompt. The generation script include the tricks proposed by by Aman Rusia to get high quality generation with memory models like Transformer-XL and XLNet (include a predefined text to make short inputs longer).

Here is how to run the script with the small version of OpenAI GPT-2 model:

python ./examples/run_glue.py \
    --model_type=gpt2 \
    --length=20 \
    --model_name_or_path=gpt2 \

Migrating from pytorch-pretrained-bert to pytorch-transformers

Here is a quick summary of what you should take care of when migrating from pytorch-pretrained-bert to pytorch-transformers

Models always output `tuples`

The main breaking change when migrating from pytorch-pretrained-bert to pytorch-transformers is that the models forward method always outputs a tuple with various elements depending on the model and the configuration parameters.

The exact content of the tuples for each model are detailled in the models' docstrings and the documentation.

In pretty much every case, you will be fine by taking the first element of the output as the output you previously used in pytorch-pretrained-bert.

Here is a pytorch-pretrained-bert to pytorch-transformers conversion example for a BertForSequenceClassification classification model:

# Let's load our model
model = BertForSequenceClassification.from_pretrained('bert-base-uncased')

# If you used to have this line in pytorch-pretrained-bert:
loss = model(input_ids, labels=labels)

# Now just use this line in pytorch-transformers to extract the loss from the output tuple:
outputs = model(input_ids, labels=labels)
loss = outputs[0]

# In pytorch-transformers you can also have access to the logits:
loss, logits = outputs[:2]

# And even the attention weigths if you configure the model to output them (and other outputs too, see the docstrings and documentation)
model = BertForSequenceClassification.from_pretrained('bert-base-uncased', output_attentions=True)
outputs = model(input_ids, labels=labels)
loss, logits, attentions = outputs

Serialization

While not a breaking change, the serialization methods have been standardized and you probably should switch to the new method save_pretrained(save_directory) if you were using any other seralization method before.

Here is an example:

### Let's load a model and tokenizer
model = BertForSequenceClassification.from_pretrained('bert-base-uncased')
tokenizer = BertTokenizer.from_pretrained('bert-base-uncased')

### Do some stuff to our model and tokenizer
# Ex: add new tokens to the vocabulary and embeddings of our model
tokenizer.add_tokens(['[SPECIAL_TOKEN_1]', '[SPECIAL_TOKEN_2]'])
model.resize_token_embeddings(len(tokenizer))
# Train our model
train(model)

### Now let's save our model and tokenizer to a directory
model.save_pretrained('./my_saved_model_directory/')
tokenizer.save_pretrained('./my_saved_model_directory/')

### Reload the model and the tokenizer
model = BertForSequenceClassification.from_pretrained('./my_saved_model_directory/')
tokenizer = BertTokenizer.from_pretrained('./my_saved_model_directory/')

Optimizers: BertAdam & OpenAIAdam are now AdamW, schedules are standard PyTorch schedules

The two optimizers previously included, BertAdam and OpenAIAdam, have been replaced by a single AdamW optimizer. The new optimizer AdamW matches PyTorch Adam optimizer API.

The schedules are now standard PyTorch learning rate schedulers and not part of the optimizer anymore.

Here is a conversion examples from BertAdam with a linear warmup and decay schedule to AdamW and the same schedule:

# Parameters:
lr = 1e-3
num_total_steps = 1000
num_warmup_steps = 100
warmup_proportion = float(num_warmup_steps) / float(num_total_steps)  # 0.1

### Previously BertAdam optimizer was instantiated like this:
optimizer = BertAdam(model.parameters(), lr=lr, schedule='warmup_linear', warmup=warmup_proportion, t_total=num_total_steps)
### and used like this:
for batch in train_data:
    loss = model(batch)
    loss.backward()
    optimizer.step()

### In PyTorch-Transformers, optimizer and schedules are splitted and instantiated like this:
optimizer = AdamW(model.parameters(), lr=lr, correct_bias=False)  # To reproduce BertAdam specific behavior set correct_bias=False
scheduler = WarmupLinearSchedule(optimizer, warmup_steps=num_warmup_steps, t_total=num_total_steps)  # PyTorch scheduler
### and used like this:
for batch in train_data:
    loss = model(batch)
    loss.backward()
    scheduler.step()
    optimizer.step()

Citation

At the moment, there is no paper associated to PyTorch-Transformers but we are working on preparing one. In the meantime, please include a mention of the library and a link to the present repository if you use this work in a published or open-source project.

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