The book presents a very detailed explanation of the Python based Natural Language Toolkit, NLTK, which is also the brain child of the authors. NLTK is a great piece of software. I have used the software off an on for the past year and half and really like how it was designed and developed by the creators.
The book builds up by explaining the usage of Python as a programming language to manipulate words, phrases and sentences. Accessing Text Corpora and direct text processing is very well described in the first hundred and twenty pages or so. Chapter six is an excellent chapter for technologist who would like to learn different ways to classify text. Although it is not in-depth, which did not seam to be the driver for the this book, it presented a simple understanding to the readers.
The concept of chunking of text and its use in classification is very well explained with examples in the book. The methods of developing context-free grammar and parsing of these CFG's probably needed a little more deeper explanation and perhaps some more examples could have helped.
Over all the book is an excellent book and I must say that it has been a very long time since I have read a book that was extremely satisfactory.
I would like to very strongly recommend this book to Python lovers who would like to explore the world of Natural Language understanding, parsing and processing. It brings out a very strong factor of Python programming language.
I give this book an "A+".