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Python 3 Text Processing with NLTK 3 Cookbook

You're reading from  Python 3 Text Processing with NLTK 3 Cookbook

Product type Book
Published in Aug 2014
Publisher
ISBN-13 9781782167853
Pages 304 pages
Edition 1st Edition
Languages
Author (1):
Jacob Perkins Jacob Perkins
Profile icon Jacob Perkins

Table of Contents (17) Chapters

Python 3 Text Processing with NLTK 3 Cookbook
Credits
About the Author
About the Reviewers
www.PacktPub.com
Preface
1. Tokenizing Text and WordNet Basics 2. Replacing and Correcting Words 3. Creating Custom Corpora 4. Part-of-speech Tagging 5. Extracting Chunks 6. Transforming Chunks and Trees 7. Text Classification 8. Distributed Processing and Handling Large Datasets 9. Parsing Specific Data Types Penn Treebank Part-of-speech Tags
Index

Training a Brill tagger


The BrillTagger class is a transformation-based tagger. It is the first tagger that is not a subclass of SequentialBackoffTagger. Instead, the BrillTagger class uses a series of rules to correct the results of an initial tagger. These rules are scored based on how many errors they correct minus the number of new errors they produce.

How to do it...

Here's a function from tag_util.py that trains a BrillTagger class using BrillTaggerTrainer. It requires an initial_tagger and train_sents.

from nltk.tag import brill, brill_trainer

def train_brill_tagger(initial_tagger, train_sents, **kwargs):
  templates = [
    brill.Template(brill.Pos([-1])),
    brill.Template(brill.Pos([1])),
    brill.Template(brill.Pos([-2])),
    brill.Template(brill.Pos([2])),
    brill.Template(brill.Pos([-2, -1])),
    brill.Template(brill.Pos([1, 2])),
    brill.Template(brill.Pos([-3, -2, -1])),
    brill.Template(brill.Pos([1, 2, 3])),
    brill.Template(brill.Pos([-1]), brill.Pos([1])),
 ...
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