API — nltk

nltk The Natural Language Toolkit (NLTK) is an open source Python library for Natural Language Processing.
nltk.classify Classes and interfaces for labeling tokens with category labels (or “class labels”).
nltk.cluster This module contains a number of basic clustering algorithms.
nltk.chunk Classes and interfaces for identifying non-overlapping linguistic groups (such as base noun phrases) in unrestricted text.
nltk.corpus NLTK corpus readers.
nltk.parse NLTK Parsers
nltk.sem NLTK Semantic Interpretation Package
nltk.stem NLTK Stemmers
nltk.tag NLTK Taggers
nltk.tokenize NLTK Tokenizer Package
nltk.twitter NLTK Twitter Package