nltk-trainer / docs / train_tagger.rst

Training Part of Speech Taggers

The script can use any corpus included with NLTK that implements a tagged_sents() method. It can also train on the timit corpus, which includes tagged sentences that are not available through the TimitCorpusReader.

Example usage can be found in Training Part of Speech Taggers with NLTK Trainer.

Train the default sequential backoff tagger on the treebank corpus::
python treebank
To use a brill tagger with the default initial tagger::
python treebank --brill
To train a NaiveBayes classifier based tagger, without a sequential backoff tagger::
python treebank --sequential '' --classifier NaiveBayes
To train a unigram tagger::
python treebank --sequential u
To train on the switchboard corpus::
python switchboard
To train on a custom corpus, whose fileids end in ".pos", using a TaggedCorpusReader::
python /path/to/corpus --reader nltk.corpus.reader.tagged.TaggedCorpusReader --fileids '.+\.pos'

The corpus path can be absolute, or relative to a nltk_data directory. For example, both corpora/treebank/tagged and /usr/share/nltk_data/corpora/treebank/tagged will work.

You can also restrict the files used with the --fileids option::
python conll2000 --fileids train.txt
For a complete list of usage options::
python --help

Using a Trained Tagger

You can use a trained tagger by loading the pickle file using
>>> import
>>> tagger ="taggers/NAME_OF_TAGGER.pickle")
Or if your tagger pickle file is not in a nltk_data subdirectory, you can load it with pickle.load::
>>> import pickle
>>> tagger = pickle.load(open("/path/to/NAME_OF_TAGGER.pickle"))

Either method will return an object that supports the TaggerI interface.

Once you have a tagger object, you can use it to tag sentences (or lists of words) with the tagger.tag(words) method::
>>> tagger.tag(['some', 'words', 'in', 'a', 'sentence'])

tagger.tag(words) will return a list of 2-tuples of the form [(word, tag)].