Best result by using Grid Search

Best_Tuning_Parameters.txt

Accuracy of MultinomialNB (naive Bayes) - 83.48868175765645

Accuracy (after tuning) of MultinomialNB (naive Bayes) - 93.27563249001332

Grid Search best score -
0.979618963226

Grid Search best parameters -
{'clf__alpha': 0.001,
 'clf__fit_prior': False,
 'tfidf__smooth_idf': True,
 'tfidf__sublinear_tf': True,
 'tfidf__use_idf': False,
 'vect__ngram_range': (1, 2)}

Metrics classification report 
                        precision    recall  f1-score   support

           alt.atheism       0.97      0.60      0.74       319
         comp.graphics       0.96      0.89      0.92       389
               sci.med       0.97      0.81      0.88       396
soc.religion.christian       0.65      0.99      0.78       398

           avg / total       0.88      0.83      0.84      1502


Metric Confusion matrix
[[192   2   6 119]
 [  2 347   4  36]
 [  2  11 322  61]
 [  2   2   1 393]]