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Neural Machine Translation with Keras.

Library documentation:

Attentional recurrent neural network NMT model

alt text

Transformer NMT model

alt text

Features (in addition to the full Keras cosmos): .


Assuming that you have pip installed and updated (>18), run:

git clone
cd nmt-keras
pip install -e .

for installing the library.


NMT-Keras requires the following libraries:

For accelerating the training and decoding on CUDA GPUs, you can optionally install:

For evaluating with additional metrics (Meteor, TER, etc), you can use the Coco-caption evaluation package and set METRICS='coco' in the file. This package requires java (version 1.8.0 or newer).



  1. Set a training configuration in the script. Each parameter is commented. See the documentation file for further info about each specific hyperparameter. You can also specify the parameters when calling the script following the syntax Key=Value

  2. Train!:



Once we have our model trained, we can translate new text using the script. Please refer to the ensembling_tutorial for more details about this script. In short, if we want to use the models from the first three epochs to translate the examples/EuTrans/test.en file, just run:

             --models trained_models/tutorial_model/epoch_1 \ 
                      trained_models/tutorial_model/epoch_2 \
             --dataset datasets/Dataset_tutorial_dataset.pkl \
             --text examples/EuTrans/test.en


The script can be used to obtain the (-log)probabilities of a parallel corpus. Its syntax is the following:

python --help
usage: Use several translation models for scoring source--target pairs
       [-h] -ds DATASET [-src SOURCE] [-trg TARGET] [-s SPLITS [SPLITS ...]]
       [-d DEST] [-v] [-c CONFIG] --models MODELS [MODELS ...]
optional arguments:
    -h, --help            show this help message and exit
    -ds DATASET, --dataset DATASET
                            Dataset instance with data
    -src SOURCE, --source SOURCE
                            Text file with source sentences
    -trg TARGET, --target TARGET
                            Text file with target sentences
    -s SPLITS [SPLITS ...], --splits SPLITS [SPLITS ...]
                            Splits to sample. Should be already includedinto the
                            dataset object.
    -d DEST, --dest DEST  File to save scores in
    -v, --verbose         Be verbose
    -c CONFIG, --config CONFIG
                            Config pkl for loading the model configuration. If not
                            specified, hyperparameters are read from
    --models MODELS [MODELS ...]
                            path to the models

Advanced features

Other features such as online learning or interactive NMT protocols are implemented in the interactiveNMT branch.



If you use this toolkit in your research, please cite:

 journal = {The Prague Bulletin of Mathematical Linguistics},
 title = {{NMT-Keras: a Very Flexible Toolkit with a Focus on Interactive NMT and Online Learning}},
 author = {\'{A}lvaro Peris and Francisco Casacuberta},
 year = {2018},
 volume = {111},
 pages = {113--124},
 doi = {10.2478/pralin-2018-0010},
 issn = {0032-6585},
 url = {}

NMT-Keras was used in a number of papers:


Much of this library has been developed together with Marc Bolaños (web page) for other sequence-to-sequence problems.

To see other projects following the same philosophy and style of NMT-Keras, take a look to:

TMA: Egocentric captioning based on temporally-linked sequences.

VIBIKNet: Visual question answering.

ABiViRNet: Video description.

Sentence SelectioNN: Sentence classification and selection.

DeepQuest: State-of-the-art models for multi-level Quality Estimation.


The Theano backend is not tested anymore, although it should work. There is a known issue with the Theano backend. When running NMT-Keras, it will show the following message:

raise theano.gof.InconsistencyError("Trying to reintroduce a removed node")
InconsistencyError: Trying to reintroduce a removed node

It is not a critical error, the model keeps working and it is safe to ignore it. However, if you want the message to be gone, use the Theano flag optimizer_excluding=scanOp_pushout_output.


Álvaro Peris (web page): [email protected]

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