This is an excellent introduction into Natural Language Processing (NLP) and caters for those with Beginner and Intermediate experience. It is a compliment to the Natural Language Toolkit, a Python library that comes with sufficient resources to really get a head round this exciting area of computer science.
For my part I purchased the book, as it looked like I would be using Python to write the tools to collect and analyse the data for my PhD. I have worked through the examples, and so far I’ve not been let down.
There is an unpublished second edition of the book, which presents NLTK version 3, and Python 3 support. This book is published under a Creative Commons License and is hosted at http://www.nltk.org/book/
Note that there is a GitHub repository for the NL Toolkit, the address being: https://github.com/nltk.