nltk.tokenize package

Submodules

Module contents

NLTK Tokenizer Package

Tokenizers divide strings into lists of substrings. For example, tokenizers can be used to find the words and punctuation in a string:

>>> from nltk.tokenize import word_tokenize
>>> s = '''Good muffins cost $3.88\nin New York.  Please buy me
... two of them.\n\nThanks.'''
>>> word_tokenize(s) 
['Good', 'muffins', 'cost', '$', '3.88', 'in', 'New', 'York', '.',
'Please', 'buy', 'me', 'two', 'of', 'them', '.', 'Thanks', '.']

This particular tokenizer requires the Punkt sentence tokenization models to be installed. NLTK also provides a simpler, regular-expression based tokenizer, which splits text on whitespace and punctuation:

>>> from nltk.tokenize import wordpunct_tokenize
>>> wordpunct_tokenize(s) 
['Good', 'muffins', 'cost', '$', '3', '.', '88', 'in', 'New', 'York', '.',
'Please', 'buy', 'me', 'two', 'of', 'them', '.', 'Thanks', '.']

We can also operate at the level of sentences, using the sentence tokenizer directly as follows:

>>> from nltk.tokenize import sent_tokenize, word_tokenize
>>> sent_tokenize(s)
['Good muffins cost $3.88\nin New York.', 'Please buy me\ntwo of them.', 'Thanks.']
>>> [word_tokenize(t) for t in sent_tokenize(s)] 
[['Good', 'muffins', 'cost', '$', '3.88', 'in', 'New', 'York', '.'],
['Please', 'buy', 'me', 'two', 'of', 'them', '.'], ['Thanks', '.']]

Caution: when tokenizing a Unicode string, make sure you are not using an encoded version of the string (it may be necessary to decode it first, e.g. with s.decode("utf8").

NLTK tokenizers can produce token-spans, represented as tuples of integers having the same semantics as string slices, to support efficient comparison of tokenizers. (These methods are implemented as generators.)

>>> from nltk.tokenize import WhitespaceTokenizer
>>> list(WhitespaceTokenizer().span_tokenize(s)) 
[(0, 4), (5, 12), (13, 17), (18, 23), (24, 26), (27, 30), (31, 36), (38, 44),
(45, 48), (49, 51), (52, 55), (56, 58), (59, 64), (66, 73)]

There are numerous ways to tokenize text. If you need more control over tokenization, see the other methods provided in this package.

For further information, please see Chapter 3 of the NLTK book.

nltk.tokenize.sent_tokenize(text, language='english')[source]

Return a sentence-tokenized copy of text, using NLTK’s recommended sentence tokenizer (currently PunktSentenceTokenizer for the specified language).

Parameters:

  • text – text to split into sentences

  • language – the model name in the Punkt corpus

nltk.tokenize.word_tokenize(text, language='english', preserve_line=False)[source]

Return a tokenized copy of text, using NLTK’s recommended word tokenizer (currently an improved TreebankWordTokenizer along with PunktSentenceTokenizer for the specified language).

Parameters:

  • text (str) – text to split into words

  • language (str) – the model name in the Punkt corpus

  • preserve_line (bool) – A flag to decide whether to sentence tokenize the text or not.