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fastText Python bindings

Project description

fastText is a library for efficient learning of word representations and sentence classification.


fastText builds on modern Mac OS and Linux distributions. Since it uses C++11 features, it requires a compiler with good C++11 support. These include :

  • (gcc-4.8 or newer) or (clang-3.3 or newer)

You will need

Building fastText

The easiest way to get the latest version of fastText is to use pip.

$ pip install fasttext

If you want to use the latest unstable release you will need to build from source using

Now you can import this library with

import fastText


In general it is assumed that the reader already has good knowledge of fastText. For this consider the main README and in particular the tutorials on our website.

We recommend you look at the examples within the doc folder.

As with any package you can get help on any Python function using the help function.

For example

+>>> import fastText
+>>> help(fastText.FastText)

Help on module fastText.FastText in fastText:


    # Copyright (c) 2017-present, Facebook, Inc.
    # All rights reserved.
    # This source code is licensed under the BSD-style license found in the
    # LICENSE file in the root directory of this source tree. An additional grant
    # of patent rights can be found in the PATENTS file in the same directory.

        Load a model given a filepath and return a model object.

        Given a string of text, tokenize it and return a list of tokens

IMPORTANT: Preprocessing data / enconding conventions

In general it is important to properly preprocess your data. In particular our example scripts in the root folder do this.

fastText assumes UTF-8 encoded text. All text must be unicode for Python2 and str for Python3. The passed text will be encoded as UTF-8 by pybind11 before passed to the fastText C++ library. This means it is important to use UTF-8 encoded text when building a model. On Unix-like systems you can convert text using iconv.

fastText will tokenize (split text into pieces) based on the following ASCII characters (bytes). In particular, it is not aware of UTF-8 whitespace. We advice the user to convert UTF-8 whitespace / word boundaries into one of the following symbols as appropiate.

  • space

  • tab

  • vertical tab

  • carriage return

  • formfeed

  • the null character

The newline character is used to delimit lines of text. In particular, the EOS token is appended to a line of text if a newline character is encountered. The only exception is if the number of tokens exceeds the MAX_LINE_SIZE constant as defined in the Dictionary header. This means if you have text that is not separate by newlines, such as the fil9 dataset, it will be broken into chunks with MAX_LINE_SIZE of tokens and the EOS token is not appended.

The length of a token is the number of UTF-8 characters by considering the leading two bits of a byte to identify subsequent bytes of a multi-byte sequence. Knowing this is especially important when choosing the minimum and maximum length of subwords. Further, the EOS token (as specified in the Dictionary header) is considered a character and will not be broken into subwords.

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