#
# Natural Language Toolkit: Sentiment Analyzer
#
# Copyright (C) 2001-2024 NLTK Project
# Author: Pierpaolo Pantone <24alsecondo@gmail.com>
# URL: <https://www.nltk.org/>
# For license information, see LICENSE.TXT
"""
Utility methods for Sentiment Analysis.
"""
import codecs
import csv
import json
import random
import re
import sys
import time
from copy import deepcopy
import nltk
from nltk.corpus import CategorizedPlaintextCorpusReader
from nltk.data import load
from nltk.tokenize import PunktTokenizer
from nltk.tokenize.casual import EMOTICON_RE
# ////////////////////////////////////////////////////////////
# { Regular expressions
# ////////////////////////////////////////////////////////////
# Regular expression for negation by Christopher Potts
NEGATION = r"""
(?:
^(?:never|no|nothing|nowhere|noone|none|not|
havent|hasnt|hadnt|cant|couldnt|shouldnt|
wont|wouldnt|dont|doesnt|didnt|isnt|arent|aint
)$
)
|
n't"""
NEGATION_RE = re.compile(NEGATION, re.VERBOSE)
CLAUSE_PUNCT = r"^[.:;!?]$"
CLAUSE_PUNCT_RE = re.compile(CLAUSE_PUNCT)
# Happy and sad emoticons
HAPPY = {
":-)",
":)",
";)",
":o)",
":]",
":3",
":c)",
":>",
"=]",
"8)",
"=)",
":}",
":^)",
":-D",
":D",
"8-D",
"8D",
"x-D",
"xD",
"X-D",
"XD",
"=-D",
"=D",
"=-3",
"=3",
":-))",
":'-)",
":')",
":*",
":^*",
">:P",
":-P",
":P",
"X-P",
"x-p",
"xp",
"XP",
":-p",
":p",
"=p",
":-b",
":b",
">:)",
">;)",
">:-)",
"<3",
}
SAD = {
":L",
":-/",
">:/",
":S",
">:[",
":@",
":-(",
":[",
":-||",
"=L",
":<",
":-[",
":-<",
"=\\",
"=/",
">:(",
":(",
">.<",
":'-(",
":'(",
":\\",
":-c",
":c",
":{",
">:\\",
";(",
}
[docs]
def timer(method):
"""
A timer decorator to measure execution performance of methods.
"""
def timed(*args, **kw):
start = time.time()
result = method(*args, **kw)
end = time.time()
tot_time = end - start
hours = tot_time // 3600
mins = tot_time // 60 % 60
# in Python 2.x round() will return a float, so we convert it to int
secs = int(round(tot_time % 60))
if hours == 0 and mins == 0 and secs < 10:
print(f"[TIMER] {method.__name__}(): {method.__name__:.3f} seconds")
else:
print(f"[TIMER] {method.__name__}(): {hours}h {mins}m {secs}s")
return result
return timed
# ////////////////////////////////////////////////////////////
# { Feature extractor functions
# ////////////////////////////////////////////////////////////
"""
Feature extractor functions are declared outside the SentimentAnalyzer class.
Users should have the possibility to create their own feature extractors
without modifying SentimentAnalyzer.
"""
# ////////////////////////////////////////////////////////////
# { Helper Functions
# ////////////////////////////////////////////////////////////
[docs]
def mark_negation(document, double_neg_flip=False, shallow=False):
"""
Append _NEG suffix to words that appear in the scope between a negation
and a punctuation mark.
:param document: a list of words/tokens, or a tuple (words, label).
:param shallow: if True, the method will modify the original document in place.
:param double_neg_flip: if True, double negation is considered affirmation
(we activate/deactivate negation scope every time we find a negation).
:return: if `shallow == True` the method will modify the original document
and return it. If `shallow == False` the method will return a modified
document, leaving the original unmodified.
>>> sent = "I didn't like this movie . It was bad .".split()
>>> mark_negation(sent)
['I', "didn't", 'like_NEG', 'this_NEG', 'movie_NEG', '.', 'It', 'was', 'bad', '.']
"""
if not shallow:
document = deepcopy(document)
# check if the document is labeled. If so, do not consider the label.
labeled = document and isinstance(document[0], (tuple, list))
if labeled:
doc = document[0]
else:
doc = document
neg_scope = False
for i, word in enumerate(doc):
if NEGATION_RE.search(word):
if not neg_scope or (neg_scope and double_neg_flip):
neg_scope = not neg_scope
continue
else:
doc[i] += "_NEG"
elif neg_scope and CLAUSE_PUNCT_RE.search(word):
neg_scope = not neg_scope
elif neg_scope and not CLAUSE_PUNCT_RE.search(word):
doc[i] += "_NEG"
return document
[docs]
def output_markdown(filename, **kwargs):
"""
Write the output of an analysis to a file.
"""
with codecs.open(filename, "at") as outfile:
text = "\n*** \n\n"
text += "{} \n\n".format(time.strftime("%d/%m/%Y, %H:%M"))
for k in sorted(kwargs):
if isinstance(kwargs[k], dict):
dictionary = kwargs[k]
text += f" - **{k}:**\n"
for entry in sorted(dictionary):
text += f" - {entry}: {dictionary[entry]} \n"
elif isinstance(kwargs[k], list):
text += f" - **{k}:**\n"
for entry in kwargs[k]:
text += f" - {entry}\n"
else:
text += f" - **{k}:** {kwargs[k]} \n"
outfile.write(text)
[docs]
def split_train_test(all_instances, n=None):
"""
Randomly split `n` instances of the dataset into train and test sets.
:param all_instances: a list of instances (e.g. documents) that will be split.
:param n: the number of instances to consider (in case we want to use only a
subset).
:return: two lists of instances. Train set is 8/10 of the total and test set
is 2/10 of the total.
"""
random.seed(12345)
random.shuffle(all_instances)
if not n or n > len(all_instances):
n = len(all_instances)
train_set = all_instances[: int(0.8 * n)]
test_set = all_instances[int(0.8 * n) : n]
return train_set, test_set
def _show_plot(x_values, y_values, x_labels=None, y_labels=None):
try:
import matplotlib.pyplot as plt
except ImportError as e:
raise ImportError(
"The plot function requires matplotlib to be installed."
"See https://matplotlib.org/"
) from e
plt.locator_params(axis="y", nbins=3)
axes = plt.axes()
axes.yaxis.grid()
plt.plot(x_values, y_values, "ro", color="red")
plt.ylim(ymin=-1.2, ymax=1.2)
plt.tight_layout(pad=5)
if x_labels:
plt.xticks(x_values, x_labels, rotation="vertical")
if y_labels:
plt.yticks([-1, 0, 1], y_labels, rotation="horizontal")
# Pad margins so that markers are not clipped by the axes
plt.margins(0.2)
plt.show()
# ////////////////////////////////////////////////////////////
# { Parsing and conversion functions
# ////////////////////////////////////////////////////////////
[docs]
def json2csv_preprocess(
json_file,
outfile,
fields,
encoding="utf8",
errors="replace",
gzip_compress=False,
skip_retweets=True,
skip_tongue_tweets=True,
skip_ambiguous_tweets=True,
strip_off_emoticons=True,
remove_duplicates=True,
limit=None,
):
"""
Convert json file to csv file, preprocessing each row to obtain a suitable
dataset for tweets Semantic Analysis.
:param json_file: the original json file containing tweets.
:param outfile: the output csv filename.
:param fields: a list of fields that will be extracted from the json file and
kept in the output csv file.
:param encoding: the encoding of the files.
:param errors: the error handling strategy for the output writer.
:param gzip_compress: if True, create a compressed GZIP file.
:param skip_retweets: if True, remove retweets.
:param skip_tongue_tweets: if True, remove tweets containing ":P" and ":-P"
emoticons.
:param skip_ambiguous_tweets: if True, remove tweets containing both happy
and sad emoticons.
:param strip_off_emoticons: if True, strip off emoticons from all tweets.
:param remove_duplicates: if True, remove tweets appearing more than once.
:param limit: an integer to set the number of tweets to convert. After the
limit is reached the conversion will stop. It can be useful to create
subsets of the original tweets json data.
"""
with codecs.open(json_file, encoding=encoding) as fp:
(writer, outf) = _outf_writer(outfile, encoding, errors, gzip_compress)
# write the list of fields as header
writer.writerow(fields)
if remove_duplicates == True:
tweets_cache = []
i = 0
for line in fp:
tweet = json.loads(line)
row = extract_fields(tweet, fields)
try:
text = row[fields.index("text")]
# Remove retweets
if skip_retweets == True:
if re.search(r"\bRT\b", text):
continue
# Remove tweets containing ":P" and ":-P" emoticons
if skip_tongue_tweets == True:
if re.search(r"\:\-?P\b", text):
continue
# Remove tweets containing both happy and sad emoticons
if skip_ambiguous_tweets == True:
all_emoticons = EMOTICON_RE.findall(text)
if all_emoticons:
if (set(all_emoticons) & HAPPY) and (set(all_emoticons) & SAD):
continue
# Strip off emoticons from all tweets
if strip_off_emoticons == True:
row[fields.index("text")] = re.sub(
r"(?!\n)\s+", " ", EMOTICON_RE.sub("", text)
)
# Remove duplicate tweets
if remove_duplicates == True:
if row[fields.index("text")] in tweets_cache:
continue
else:
tweets_cache.append(row[fields.index("text")])
except ValueError:
pass
writer.writerow(row)
i += 1
if limit and i >= limit:
break
outf.close()
# ////////////////////////////////////////////////////////////
# { Demos
# ////////////////////////////////////////////////////////////
[docs]
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,
)
[docs]
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.corpus import subjectivity
from nltk.sentiment import SentimentAnalyzer
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:
sentim_analyzer.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
[docs]
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))
[docs]
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"]
)
[docs]
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))
if __name__ == "__main__":
from sklearn.svm import LinearSVC
from nltk.classify import MaxentClassifier, NaiveBayesClassifier
from nltk.classify.scikitlearn import SklearnClassifier
from nltk.twitter.common import _outf_writer, extract_fields
naive_bayes = NaiveBayesClassifier.train
svm = SklearnClassifier(LinearSVC()).train
maxent = MaxentClassifier.train
demo_tweets(naive_bayes)
# demo_movie_reviews(svm)
# demo_subjectivity(svm)
# demo_sent_subjectivity("she's an artist , but hasn't picked up a brush in a year . ")
# demo_liu_hu_lexicon("This movie was actually neither that funny, nor super witty.", plot=True)
# demo_vader_instance("This movie was actually neither that funny, nor super witty.")
# demo_vader_tweets()