python - Save Naive Bayes Trained Classifier in NLTK

48
votes

I'm slightly confused in regard to how I save a trained classifier. As in, re-training a classifier each time I want to use it is obviously really bad and slow, how do I save it and the load it again when I need it? Code is below, thanks in advance for your help. I'm using Python with NLTK Naive Bayes Classifier. 

classifier = nltk.NaiveBayesClassifier.train(training_set)
# look inside the classifier train method in the source code of the NLTK library

def train(labeled_featuresets, estimator=nltk.probability.ELEProbDist):
    # Create the P(label) distribution
    label_probdist = estimator(label_freqdist)
    # Create the P(fval|label, fname) distribution
    feature_probdist = {}
    return NaiveBayesClassifier(label_probdist, feature_probdist)
3
pythonmachine-learningclassificationnltknaivebayes
Are you asking for some kind of persistence strategy? As in save to DB, file and load again? You could just pickle the data and load it again later. – EdChum

3 Answers

91
votes

To save:

import pickle
f = open('my_classifier.pickle', 'wb')
pickle.dump(classifier, f)
f.close()

To load later:

import pickle
f = open('my_classifier.pickle', 'rb')
classifier = pickle.load(f)
f.close()
5
votes

I went thru the same problem, and you cannot save the object since is a ELEFreqDistr NLTK class. Anyhow NLTK is hell slow. Training took 45 mins on a decent set and I decided to implement my own version of the algorithm (run it with pypy or rename it .pyx and install cython). It takes about 3 minutes with the same set and it can simply save data as json (I'll implement pickle which is faster/better).

I started a simple github project, check out the code here

1
votes

To Retrain the Pickled Classifer :

f = open('originalnaivebayes5k.pickle','rb')
classifier = pickle.load(f)
classifier.train(training_set)
print('Accuracy:',nltk.classify.accuracy(classifier,testing_set)*100)
f.close()