NLTK Source
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Latest commit 8dde9e7 Oct 11, 2016 @stevenbird stevenbird committed on GitHub Merge pull request #1473 from timleslie/develop
Fix undefined variable bugs

Natural Language Toolkit (NLTK)

NLTK -- the Natural Language Toolkit -- is a suite of open source Python modules, data sets and tutorials supporting research and development in Natural Language Processing.

For documentation, please visit


Do you want to contribute with NLTK development? Great! Please read more details at

See also How to contribute to NLTK.


Have you found the toolkit helpful? Please support NLTK development by donating to the project via PayPal, using the link on the NLTK homepage.


If you publish work that uses NLTK, please cite the NLTK book, as follows:

Bird, Steven, Edward Loper and Ewan Klein (2009).
Natural Language Processing with Python.  O'Reilly Media Inc.


Copyright (C) 2001-2016 NLTK Project

For license information, see LICENSE.txt. have a list of everyone contributed to NLTK.


  • NLTK source code is distributed under the Apache 2.0 License.
  • NLTK documentation is distributed under the Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 United States license.
  • NLTK corpora are provided under the terms given in the README file for each corpus; all are redistributable, and available for non-commercial use.
  • NLTK may be freely redistributed, subject to the provisions of these licenses.