Character Based CNN

This repo contains a PyTorch implementation of a character-level convolutional neural network for text classification.

The model architecture comes from this paper:

There are two variants: a large and a small. You can switch between the two by changing the configuration file.

This architecture has 6 convolutional layers:

Layer Large Feature Small Feature Kernel Pool
1 1024 256 7 3
2 1024 256 7 3
3 1024 256 3 N/A
4 1024 256 3 N/A
5 1024 256 3 N/A
6 1024 256 3 3

and 2 fully connected layers:

Layer Output Units Large Output Units Small
7 2048 1024
8 2048 1024
9 Depends on the problem Depends on the problem

Video tutorial

If you're interested in how character CNN work as well as in the demo of this project you can check my youtube video tutorial.

Why you should care about character level CNNs

They have very nice properties:

  • They are quite powerful in text classification (see paper's benchmark) even though they don't have any notion of semantics
  • You don't need to apply any text preprocessing (tokenization, lemmatization, stemming ...) while using them
  • They handle misspelled words and OOV (out-of-vocabulary) tokens
  • They are faster to train compared to recurrent neural networks
  • They are lightweight since they don't require storing a large word embedding matrix. Hence, you can deploy them in production easily

Training a sentiment classifier on french customer reviews

I have tested this model on a set of french labeled customer reviews (of over 3 millions rows). I reported the metrics in TensorboardX.

I got the following results

F1 score Accuracy
train 0.965 0.9366
test 0.945 0.915



  • numpy
  • pandas
  • sklearn
  • PyTorch 0.4.1
  • tensorboardX
  • Tensorflow (to be able to run TensorboardX)

Structure of the code

At the root of the project, you will have:

  • used for training a model
  • used for the testing and inference
  • config.json: a configuration file for storing model parameters (number of filters, neurons)
  • src: a folder that contains:
    • the actual CNN model (model initialization and forward method)
    • the script responsible of passing the data to the training after processing it
    • a set of utility functions for text preprocessing (url/hashtag/user_mention removal)

How to use the code


The code currently works only on binary labels (0/1)

Launch with the following arguments:

  • data_path: path of the data. Data should be in csv format with at least a column for text and a column for the label
  • validation_split: the ratio of validation data. default to 0.2
  • label_column: column name of the labels
  • text_column: column name of the texts
  • max_rows: the maximum number of rows to load from the dataset. (I mainly use this for testing to go faster)
  • chunksize: size of the chunks when loading the data using pandas. default to 500000
  • encoding: default to utf-8
  • steps: text preprocessing steps to include on the text like hashtag or url removal
  • group_labels: whether or not to group labels. Default to None.
  • use_sampler: whether or not to use a weighted sampler to overcome class imbalance
  • alphabet: default to abcdefghijklmnopqrstuvwxyz0123456789,;.!?:'"/\|[email protected]#$%^&*~`+-=<>()[]{} (normally you should not modify it)
  • number_of_characters: default 70
  • extra_characters: additional characters that you'd add to the alphabet. For example uppercase letters or accented characters
  • max_length: the maximum length to fix for all the documents. default to 150 but should be adapted to your data
  • epochs: number of epochs
  • batch_size: batch size, default to 128.
  • optimizer: adam or sgd, default to sgd
  • learning_rate: default to 0.01
  • class_weights: whether or not to use class weights in the cross entropy loss
  • focal_loss: whether or not to use the focal loss
  • gamma: gamma parameter of the focal loss. default to 2
  • alpha: alpha parameter of the focal loss. default to 0.25
  • schedule: number of epochs by which the learning rate decreases by half (learning rate scheduling works only for sgd), default to 3. set it to 0 to disable it
  • patience: maximum number of epochs to wait without improvement of the validation loss, default to 3
  • early_stopping: to choose whether or not to early stop the training. default to 0. set to 1 to enable it.
  • checkpoint: to choose to save the model on disk or not. default to 1, set to 0 to disable model checkpoint
  • workers: number of workers in PyTorch DataLoader, default to 1
  • log_path: path of tensorboard log file
  • output: path of the folder where models are saved
  • model_name: prefix name of saved models

Example usage:

python --data_path=/data/tweets.csv --max_rows=200000

Plotting results to TensorboardX

Run this command at the root of the project:

tensorboard --logdir=./logs/ --port=6006

Then go to: http://localhost:6006 (or whatever host you're using)


Launch with the following arguments:

  • model: path of the pre-trained model
  • text: input text
  • steps: list of preprocessing steps, default to lower
  • alphabet: default to 'abcdefghijklmnopqrstuvwxyz0123456789-,;.!?:'"\/|[email protected]#$%^&*~`+-=<>()[]{}\n'
  • number_of_characters: default to 70
  • extra_characters: additional characters that you'd add to the alphabet. For example uppercase letters or accented characters
  • max_length: the maximum length to fix for all the documents. default to 150 but should be adapted to your data

Example usage:

python ./models/pretrained_model.pth --text="I love pizza !" --max_length=150

Download pretrained models

  • Sentiment analysis model on French customer reviews (3M documents): download link

    When using it:

    • set max_length to 300
    • use extra_characters="éàèùâêîôûçëïü" (accented letters)