Open source Python modules, linguistic data and documentation for research and development in natural language processing, supporting dozens of NLP tasks, with distributions for Windows, Mac OSX and Linux. NLTK comes with many corpora, toy grammars, trained models, etc. A complete list is posted at: http://nltk.googlecode.com/svn/trunk/nltk_data/index.xml To retrieve all the data, use "python -m nltk.downloader all". This package requires PyYAML.