我们从Python开源项目中，提取了以下30个代码示例，用于说明如何使用nltk.sentiment()。
def demo_sent_subjectivity(text): """ Classify a single sentence as subjective or objective using a stored SentimentAnalyzer. :param text: a sentence whose subjectivity has to be classified. """ from nltk.classify import NaiveBayesClassifier from nltk.tokenize import regexp word_tokenizer = regexp.WhitespaceTokenizer() try: sentim_analyzer = load('sa_subjectivity.pickle') except LookupError: print('Cannot find the sentiment analyzer you want to load.') print('Training a new one using NaiveBayesClassifier.') sentim_analyzer = demo_subjectivity(NaiveBayesClassifier.train, True) # Tokenize and convert to lower case tokenized_text = [word.lower() for word in word_tokenizer.tokenize(text)] print(sentim_analyzer.classify(tokenized_text))
def demo_liu_hu_lexicon(sentence, plot=False): """ Basic example of sentiment classification using Liu and Hu opinion lexicon. This function simply counts the number of positive, negative and neutral words in the sentence and classifies it depending on which polarity is more represented. Words that do not appear in the lexicon are considered as neutral. :param sentence: a sentence whose polarity has to be classified. :param plot: if True, plot a visual representation of the sentence polarity. """ from nltk.corpus import opinion_lexicon from nltk.tokenize import treebank tokenizer = treebank.TreebankWordTokenizer() pos_words = 0 neg_words = 0 tokenized_sent = [word.lower() for word in tokenizer.tokenize(sentence)] x = list(range(len(tokenized_sent))) # x axis for the plot y = [] for word in tokenized_sent: if word in opinion_lexicon.positive(): pos_words += 1 y.append(1) # positive elif word in opinion_lexicon.negative(): neg_words += 1 y.append(-1) # negative else: y.append(0) # neutral if pos_words > neg_words: print('Positive') elif pos_words < neg_words: print('Negative') elif pos_words == neg_words: print('Neutral') if plot == True: _show_plot(x, y, x_labels=tokenized_sent, y_labels=['Negative', 'Neutral', 'Positive'])
def demo_vader_instance(text): """ Output polarity scores for a text using Vader approach. :param text: a text whose polarity has to be evaluated. """ from nltk.sentiment import SentimentIntensityAnalyzer vader_analyzer = SentimentIntensityAnalyzer() print(vader_analyzer.polarity_scores(text))
def demo_movie_reviews(trainer, n_instances=None, output=None): """ Train classifier on all instances of the Movie Reviews dataset. The corpus has been preprocessed using the default sentence tokenizer and WordPunctTokenizer. Features are composed of: - most frequent unigrams :param trainer: `train` method of a classifier. :param n_instances: the number of total reviews that have to be used for training and testing. Reviews will be equally split between positive and negative. :param output: the output file where results have to be reported. """ from nltk.corpus import movie_reviews from nltk.sentiment import SentimentAnalyzer if n_instances is not None: n_instances = int(n_instances/2) pos_docs = [(list(movie_reviews.words(pos_id)), 'pos') for pos_id in movie_reviews.fileids('pos')[:n_instances]] neg_docs = [(list(movie_reviews.words(neg_id)), 'neg') for neg_id in movie_reviews.fileids('neg')[:n_instances]] # We separately split positive and negative instances to keep a balanced # uniform class distribution in both train and test sets. train_pos_docs, test_pos_docs = split_train_test(pos_docs) train_neg_docs, test_neg_docs = split_train_test(neg_docs) training_docs = train_pos_docs+train_neg_docs testing_docs = test_pos_docs+test_neg_docs sentim_analyzer = SentimentAnalyzer() all_words = sentim_analyzer.all_words(training_docs) # Add simple unigram word features unigram_feats = sentim_analyzer.unigram_word_feats(all_words, min_freq=4) sentim_analyzer.add_feat_extractor(extract_unigram_feats, unigrams=unigram_feats) # Apply features to obtain a feature-value representation of our datasets training_set = sentim_analyzer.apply_features(training_docs) test_set = sentim_analyzer.apply_features(testing_docs) classifier = sentim_analyzer.train(trainer, training_set) try: classifier.show_most_informative_features() except AttributeError: print('Your classifier does not provide a show_most_informative_features() method.') results = sentim_analyzer.evaluate(test_set) if output: extr = [f.__name__ for f in sentim_analyzer.feat_extractors] output_markdown(output, Dataset='Movie_reviews', Classifier=type(classifier).__name__, Tokenizer='WordPunctTokenizer', Feats=extr, Results=results, Instances=n_instances)
def demo_subjectivity(trainer, save_analyzer=False, n_instances=None, output=None): """ Train and test a classifier on instances of the Subjective Dataset by Pang and Lee. The dataset is made of 5000 subjective and 5000 objective sentences. All tokens (words and punctuation marks) are separated by a whitespace, so we use the basic WhitespaceTokenizer to parse the data. :param trainer: `train` method of a classifier. :param save_analyzer: if `True`, store the SentimentAnalyzer in a pickle file. :param n_instances: the number of total sentences that have to be used for training and testing. Sentences will be equally split between positive and negative. :param output: the output file where results have to be reported. """ from nltk.sentiment import SentimentAnalyzer from nltk.corpus import subjectivity if n_instances is not None: n_instances = int(n_instances/2) subj_docs = [(sent, 'subj') for sent in subjectivity.sents(categories='subj')[:n_instances]] obj_docs = [(sent, 'obj') for sent in subjectivity.sents(categories='obj')[:n_instances]] # We separately split subjective and objective instances to keep a balanced # uniform class distribution in both train and test sets. train_subj_docs, test_subj_docs = split_train_test(subj_docs) train_obj_docs, test_obj_docs = split_train_test(obj_docs) training_docs = train_subj_docs+train_obj_docs testing_docs = test_subj_docs+test_obj_docs sentim_analyzer = SentimentAnalyzer() all_words_neg = sentim_analyzer.all_words([mark_negation(doc) for doc in training_docs]) # Add simple unigram word features handling negation unigram_feats = sentim_analyzer.unigram_word_feats(all_words_neg, min_freq=4) sentim_analyzer.add_feat_extractor(extract_unigram_feats, unigrams=unigram_feats) # Apply features to obtain a feature-value representation of our datasets training_set = sentim_analyzer.apply_features(training_docs) test_set = sentim_analyzer.apply_features(testing_docs) classifier = sentim_analyzer.train(trainer, training_set) try: classifier.show_most_informative_features() except AttributeError: print('Your classifier does not provide a show_most_informative_features() method.') results = sentim_analyzer.evaluate(test_set) if save_analyzer == True: save_file(sentim_analyzer, 'sa_subjectivity.pickle') if output: extr = [f.__name__ for f in sentim_analyzer.feat_extractors] output_markdown(output, Dataset='subjectivity', Classifier=type(classifier).__name__, Tokenizer='WhitespaceTokenizer', Feats=extr, Instances=n_instances, Results=results) return sentim_analyzer
