NLTK Cheat Sheet

NLTK natural language toolkit reference covering tokenization, stopword removal, stemming, lemmatization, part-of-speech tagging, and named entity chunking.

2 PagesBeginnerApr 8, 2026

Tokenization

Split text into sentences and words.

python

import nltknltk.download("punkt")nltk.download("stopwords")nltk.download("averaged_perceptron_tagger")from nltk.tokenize import word_tokenize, sent_tokenizetext = "NLTK is a leading platform for building Python NLP programs."sentences = sent_tokenize(text)words = word_tokenize(text)

Stopwords, Stemming & Lemmatization

Normalize tokens for downstream tasks.

python

from nltk.corpus import stopwordsfrom nltk.stem import PorterStemmer, WordNetLemmatizerstop_words = set(stopwords.words("english"))filtered = [w for w in words if w.lower() not in stop_words]stemmer = PorterStemmer()stemmed = [stemmer.stem(w) for w in filtered]          # e.g. "running" -> "run"lemmatizer = WordNetLemmatizer()lemmas = [lemmatizer.lemmatize(w) for w in filtered]     # dictionary-form words

POS Tagging & Named Entities

Tag parts of speech and chunk entities.

python

from nltk import pos_tag, ne_chunktagged = pos_tag(word_tokenize("Apple is looking at buying a UK startup."))# [('Apple', 'NNP'), ('is', 'VBZ'), ('looking', 'VBG'), ...]tree = ne_chunk(tagged)      # named entity chunks: PERSON, ORGANIZATION, GPEprint(tree)

Key Modules

Main areas of the NLTK library.

nltk.tokenize- splits text into sentences/words
nltk.corpus- built-in corpora and lexicons (stopwords, wordnet, movie_reviews)
nltk.stem- PorterStemmer, SnowballStemmer, WordNetLemmatizer
nltk.tag- part-of-speech tagging
nltk.chunk- shallow parsing / named entity chunking
nltk.classify- Naive Bayes and other text classifiers
nltk.sentiment- VADER sentiment analyzer (SentimentIntensityAnalyzer)

Pro Tip

Call nltk.download() for each resource you use (punkt, stopwords, wordnet, etc.) once per environment before running tokenizers or taggers — NLTK ships as a thin library with its data downloaded separately, so a fresh install raises LookupError until resources are fetched.

Was this cheat sheet helpful?

OpenCV Cheat Sheet

spaCy Cheat Sheet