The pattern.en module contains a fast part-of-speech tagger for English (identifies nouns, adjectives, verbs, etc. in a sentence), sentiment analysis, tools for English verb conjugation and noun singularization & pluralization, and a WordNet interface.

It can be used by itself or with other pattern modules: web | db | en | search | vector | graph.



Indefinite article

The article is the most common determiner (DT) in English. It defines whether the successive noun is definite (the cat) or indefinite (a cat). The definite article is always the. The indefinite article can be a or an depending on how the successive noun is pronounced.

article(word, function=INDEFINITE)   # DEFINITE | INDEFINITE
referenced(word, article=INDEFINITE) # Returns article + word.
>>> from pattern.en import referenced
>>> print referenced('university')
>>> print referenced('hour')

a university
an hour

Reference: Granger, M. (2006). Ruby Linguistics Framework,


Pluralization + singularization

The pluralize() function returns the singular form of a plural noun. The singularize() function returns the plural form of a singular noun. The pos parameter (part-of-speech) can be set to NOUN or ADJECTIVE, but only a small number of possessive adjectives inflect (e.g. myour). The custom dictionary is for user-defined replacements. Accuracy is 96%.

pluralize(word, pos=NOUN, custom={}, classical=True)
singularize(word, pos=NOUN, custom={})
>>> from pattern.en import pluralize, singularize
>>> print pluralize('child')
>>> print singularize('wolves')


Conway, D. (1998). An Algorithmic Approach to English Pluralization. Proceedings of the 2nd Perl conference.
Ferrer, B. (2005). Inflector for Python,


Comparative + superlative

The comparative() and superlative() functions give the comparative or superlative form of an adjective. Words with three or more syllables (e.g., fantastic) are simply preceded by more or most.

comparative(adjective)      # big => bigger
superlative(adjective)      # big => biggest
>>> from pattern.en import comparative, superlative
>>> print comparative('bad')
>>> print superlative('bad')



Verb conjugation

The pattern.en module has a lexicon of 8,500 common English verbs and their conjugated forms (infinitive, 3rd singular present, present participle, past and past participle – verbs such as be may have more forms). Some verbs can also be negated, including be, can, do, will, must, have, may, need, dare, ought.

   person = 3,              # 1, 2, 3 or None
   number = SINGULAR,       # SG, PL
  negated = False,          # True or False
    parse = True) 
lemma(verb)                 # Base form, e.g., are => be.
lexeme(verb)                # List of possible forms: be => is, was, ...
tenses(verb)                # List of possible tenses of the given form.

The conjugate() function takes the following optional parameters:

Tense Person Number Mood Aspect Alias Tag Example
INFINITIVE None None None None "inf" VB be
PAST None None None None "p" VBD were

Instead of optional parameters, a single short alias, the part-of-speech tag, or PARTICIPLE or PAST+PARTICIPLE can also be given. With no parameters, the infinitive form of the verb is returned.

For example:

>>> from pattern.en import conjugate, lemma, lexeme
>>> print lexeme('purr')
>>> print lemma('purring')
>>> print conjugate('purred', '3sg') # he / she / it

['purr', 'purrs', 'purring', 'purred']
>>> from pattern.en import tenses, PAST, PL
>>> print 'p' in tenses('purred') # By alias.
>>> print PAST in tenses('purred')
>>> print (PAST, 1, PL) in tenses('purred')


Reference: XTAG English morphology (1999), University of Pennsylvania,

Rule-based conjugation

All verb functions have an optional parse parameter (True by default) that enables a rule-based parser for unknown verbs. This will not work for irregular verbs, and it is fragile for verbs ending in -e in the past tense, or the present participle. The overall accuracy of the algorithm is 91%.

With parse=Falseconjugate() and lemma() yield None:

>>> from pattern.en import verbs, conjugate, PARTICIPLE
>>> print 'google'  in verbs.infinitives
>>> print 'googled' in verbs.inflections
>>> print conjugate('googled', tense=PARTICIPLE, parse=False)
>>> print conjugate('googled', tense=PARTICIPLE, parse=True)




The number() function returns a float or int parsed from the given (numeric) string. If no number can be parsed from the string, it returns 0.

The numerals() function returns the given int or float as a string of numerals. By default, the fraction is rounded to two decimals.

The quantify() function returns a word count approximation. Two similar words are a pair, three to eight several, and so on. Words can be given as a list, a word → count dictionary, or as a single word + amount.

The reflect() function quantifies Python objects – see the examples bundled with the module.

number(string)              # "seventy-five point two" => 75.2
numerals(n, round=2)        # 2.245 => "two point twenty-five"
quantify([word1, word2, ...], plural={})
reflect(object, quantify=True, replace=[])
>>> from pattern.en import quantify
>>> print quantify(['goose', 'goose', 'duck', 'chicken', 'chicken', 'chicken'])
>>> print quantify({'carrot': 100, 'parrot': 20})
>>> print quantify('carrot', amount=1000)

several chickens, a pair of geese an⁣d a duck
dozens of carrots an⁣d a score of parrots
hundreds of carrots 



The suggest() function returns a list of spelling suggestions for a given word. Each suggestion is a (word, confidence)-tuple. It is about 70% accurate.

>>> from pattern.en import suggest
>>> print suggest("parot")

[("part", 0.99), ("parrot", 0.01)]

Reference: Norvig, P. (2007). How to Write a Spelling Corrector. 



The ngrams() function returns a list of n-grams (i.e., tuples of n successive words) from the given string. Alternatively, you can supply a Text or Sentence object (see further). Punctuation marks are stripped from words, and n-grams will not run over sentence delimiters (i.e., .!?), unless continuous is True.

ngrams(string, n=3, punctuation=".,;:!?()[]{}`''\"@#$^&*+-|=~_", continuous=False)
>>> from pattern.en import ngrams
>>> print ngrams("I am eating pizza.", n=2) # bigrams

[('I', 'am'), ('am', 'eating'), ('eating', 'pizza')] 



A parser identifies sentences, words and word types in a string of text. This involves tokenization (distinguishing between abbreviations and sentence breaks), part-of-speech tagging (annotating words with their type, e.g., is can a noun or a verb?) and chunking (grouping consecutive words that belong together). Parsing can be used to answer questions such as who did what and why and is useful in a wide range of text mining applications. The pattern.en parser uses a lexicon of a 100,000 known words and their part-of-speech tag, along with rules for unknown words based on word suffix (e.g., -ly = ADVERB) and context (surrounding words). This approach is fast but not always accurate, since many words are ambiguous and hard to capture with simple rules. The overall accuracy is about 95% (95.8% on WSJ portions 22-24). It is lower for informal language use (e.g., chat language).

The parse() function takes a string of text and returns a part-of-speech tagged Unicode string. Sentences in the output are separated by newline characters.

   tokenize = True,         # Split punctuation marks from words?
       tags = True,         # Parse part-of-speech tags? (NN, JJ, ...)
     chunks = True,         # Parse chunks? (NP, VP, PNP, ...)
  relations = False,        # Parse chunk relations? (-SBJ, -OBJ, ...)
    lemmata = False,        # Parse lemmata? (ate => eat)
   encoding = 'utf-8'       # Input string encoding.
     tagset = None)         # Penn Treebank II (default) or UNIVERSAL.

For example:

>>> from pattern.en import parse
>>> print parse('I eat pizza with a fork.')

I/PRP/B-NP/O eat/VBD/B-VP/O pizza/NN/B-NP/O with/IN/B-PP/B-PNP a/DT/B-NP/I-PNP
fork/NN/I-NP/I-PNP ././O/O
  • With tags=True each word is annotated with a part-of-speech tag. 
  • With chunks=True each word is annotated with a chunk tag and a PNP tag (prepositional noun phrase, PP + NP). The O tag (= outside) means that the word is not part of a chunk.
  • With relations=True each word is annotated with a role tag (e.g., -SBJ for subject or -OBJ for).
  • With lemmata=True each word is annotated with its base form. 
  • With tokenize=False, punctuation marks will not be separated from words.
    The input string is expected to be tokenized beforehand, or sentence delimiters are not discovered.

Reference: Brill, E. (1992). A simple rule-based part of speech tagger. ANLC '92 Proceedings.

Parser tags

Let's examine the word fork and the tags assigned by the parser in the example above:

word part-of-speech chunk pnp
fork NN I-NP I-PNP

The word's part-of-speech tag is NN, which means that it is a noun. The word occurs in a NP chunk, a noun phrase (i.e., a fork). It is also part of a prepositional noun phrase (i.e., with a fork).

Common part-of-speech tags are NN (noun), VB (verb), JJ (adjective), RB (adverb) and IN (preposition).
Common chunk tags are NP (noun phrase) and VP (verb phrase).
Common chunk relations are NP-SBJ (subject) and NP-OBJ (object).

The Penn Treebank II tagset gives an overview of all the possible tags generated by the parser.

Parser tagger & tokenizer

The tokenize() function returns a list of sentences, with punctuation marks split from words. It takes an optional replace dictionary, by default used to split contractions, i.e., {"'ve": 've", ...}.

The tag() function simply annotates words with their part-of-speech tag and returns a list of (word, tag)-tuples:

tokenize(string, punctuation=".,;:!?()[]{}`''\"@#$^&*+-|=~_", replace={})
tag(string, tokenize=True, encoding='utf-8')
>>> from pattern.en import tag
>>> for word, pos in tag('I feel *happy*!') 
>>>     if pos == "JJ": # Retrieve all adjectives.
>>>         print word


Parser output

The output of parse() is a string of sentences in which each word has been annotated with the requested tags. The pprint() function gives a human-readable breakdown of the tags (the extra p- is for pretty).

>>> from pattern.en import parse
>>> from pattern.en import pprint 
>>> pprint(parse('I ate pizza.', relations=True, lemmata=True))

    WORD   TAG    CHUNK   ROLE   ID     PNP    LEMMA
       I   PRP    NP      SBJ    1      -      i   
     ate   VBP    VP      -      1      -      eat         
   pizza   NN     NP      OBJ    1      -      pizza         
       .   .      -       -      -      -      .        

The output of parse() is a subclass of unicode called TaggedString whose TaggedString.split() method by default yields a list of sentences, where each sentence is a list of tokens, where each token is a list of the word + its tags.

>>> from pattern.en import parse
>>> print parse('I ate pizza.').split()

[[[u'I', u'PRP', u'B-NP', u'O'], 
  [u'ate', u'VBD', u'B-VP', u'O'], 
  [u'pizza', u'NN', u'B-NP', u'O'], 
  [u'.', u'.', u'O', u'O']]]     

The most convenient way to analyze and mine the output is to construct a parse tree.


Parse trees

A parse tree stores a tagged string as a tree of nested objects that can be traversed to analyze the constituents in the text. The parsetree() function takes the same parameters as parse() and returns a Text object. A Text is a list of Sentence objects. Each Sentence is a list of Word objects. Word objects can be grouped in Chunk objects, which are related to other Chunk objects.

   tokenize = True,         # Split punctuation marks from words?
       tags = True,         # Parse part-of-speech tags? (NN, JJ, ...)
     chunks = True,         # Parse chunks? (NP, VP, PNP, ...)
  relations = False,        # Parse chunk relations? (-SBJ, -OBJ, ...)
    lemmata = False,        # Parse lemmata? (ate => eat)
   encoding = 'utf-8'       # Input string encoding.
     tagset = None)         # Penn Treebank II (default) or UNIVERSAL.

The following example shows the parse tree for the sentence "The cat sat on the mat.":

>>> from pattern.en import parsetree
>>> s = parsetree('The cat sat on the mat.', relations=True, lemmata=True)
>>> print repr(s)

>>> for sentence in s:
>>>     for chunk in sentence.chunks:
>>>         print chunk.type, [(w.string, w.type) for w in chunk.words]

NP [(u'the', u'DT'), (u'cat', u'NN')]
VP [(u'sat', u'VBD')]
PP [(u'on', u'IN')]
NP [(u'the', 'DT), (u'mat', u'NN')] 

A common approach is to store output from parse() in a .txt file, with a tagged sentence on each line. The tree() function can be used to load it as a Text object. It has an optional token parameter that defines the format of the tokens (tagged words). So parsetree(s) is the same as tree(parse(s)).

tree(taggedstring, token=[WORD, POS, CHUNK, PNP, REL, LEMMA])
>>> from pattern.en import tree
>>> for sentence in tree(open('tagged.txt'), token=[WORD, POS, CHUNK]) 
>>>     print sentence


A Text is a list of Sentence objects (i.e., it can be iterated with for sentence in text:).

text = Text(taggedstring, token=[WORD, POS, CHUNK, PNP, REL, LEMMA])
text = Text.from_xml(xml)  # Reads an XML string generated with Text.xml.
text.string                # 'The cat sat on the mat .'
text.sentences             # [Sentence('The cat sat on the mat .')]


A Sentence is a list of Word objects, with attributes and methods that group words in Chunk objects.

sentence = Sentence(taggedstring, token=[WORD, POS, CHUNK, PNP, REL, LEMMA])
sentence = Sentence.from_xml(xml) 
sentence.parent            # Sentence parent, or None.                # Unique id for each sentence.
sentence.start             # 0
sentence.stop              # len(Sentence).
sentence.string            # Tokenized string, without tags. 
sentence.words             # List of Word objects. 
sentence.lemmata           # List of word lemmata. 
sentence.chunks            # List of Chunk objects.
sentence.subjects          # List of NP-SBJ chunks.
sentence.objects           # List of NP-OBJ chunks.
sentence.verbs             # List of VP chunks.
sentence.relations         # {'SBJ': {1: Chunk('the cat/NP-SBJ-1')},
                           #   'VP': {1: Chunk('sat/VP-1')},
                           #  'OBJ': {}}
sentence.pnp               # List of PNPChunks: [Chunk('on the mat/PNP')]
sentence.slice(start, stop)
  • Sentence.constituents() returns a mixed, in-order list of Word and Chunk objects.
    With pnp=True, it will yield PNPChunk objects whenever possible.
  • Sentence.slice() returns a Slice (= a subclass of Sentence) starting with the word at index start and containing all words up to (not including) index stop.

Sentence words

A Sentence is made up of Word objects, which are also grouped in Chunk objects:

word = Word(sentence, string, lemma=None, type=None, index=0)
word.sentence              # Sentence parent.
word.index                 # Sentence index of word.
word.string                # String (Unicode).
word.lemma                 # String lemma, e.g. 'sat' => 'sit',
word.type                  # Part-of-speech tag (NN, JJ, VBD, ...)
word.chunk                 # Chunk parent, or None.
word.pnp                   # PNPChunk parent, or None.

Sentence chunks

A Chunk is a list of Word objects that belong together.
Multiple chunks can be part of a PNPChunk, which start with a PP chunk followed by NP chunks.

chunk = Chunk(sentence, words=[], type=None, role=None, relation=None)
chunk.sentence             # Sentence parent.
chunk.start                # Sentence index of first word.
chunk.stop                 # Sentence index of last word + 1.
chunk.string               # String of words (Unicode).
chunk.words                # List of Word objects.
chunk.lemmata              # List of word lemmata. 
chunk.head                 # Primary Word in the chunk.
chunk.type                 # Chunk tag (NP, VP, PP, ...)
chunk.role                 # Role tag (SBJ, OBJ, ...)
chunk.relation             # Relation id, e.g. NP-SBJ-1 => 1.
chunk.relations            # List of (id, role)-tuples.
chunk.related              # List of Chunks with same relation id.
chunk.subject              # NP-SBJ chunk with same id.
chunk.object               # NP-OBJ chunk with same id.
chunk.verb                 # VP chunk with same id.
chunk.modifiers            # []
chunk.conjunctions         # []
chunk.pnp                  # PNPChunk parent, or None.
  • Chunk.head yields the primary Word in the chunk: the big catcat.
  • Chunk.relations contains all relations the chunk is part of.
    Some chunks have multiple relations, e.g., SBJ as well as OBJ, or OBJ of multiple VP's.
  • For VP chunks, Chunk.modifiers is a list of nearby adjectives and adverbs that have no relations.
    For example, in the cat purred happily, modifier of purred → happily.
  • Chunk.conjunctions is a list of chunks linked by and and or to this chunk.
    For example in up and down: the up chunk has conjunctions: [(Chunk('down'), AND)].

Prepositional noun phrases

A PNPChunk or prepositional noun phrase is a subclass of Chunk. It groups PP + NP chunks (= PNP).

pnp = PNPChunk(sentence, words=[], type=None, role=None, relation=None)
pnp.string                 # String of words (Unicode).
pnp.chunks                 # List of Chunk objects.
pnp.preposition            # First PP chunk in the PNP.

Words and chunks that are part of a PNP will have their Word.pnp and Chunk.pnp attribute set. All prepositional noun phrases in a sentence can be retrieved with Sentence.pnp.



Written text can be broadly categorized into two types: facts and opinions. Opinions carry people's sentiments, appraisals and feelings toward the world. The pattern.en module bundles a lexicon of adjectives (e.g., good, bad, amazing, irritating, ...) that occur frequently in product reviews, annotated with scores for sentiment polarity (positive ↔ negative) and subjectivity (objective ↔ subjective). 

The sentiment() function returns a (polarity, subjectivity)-tuple for the given sentence, based on the adjectives it contains, where polarity is a value between -1.0 and +1.0 and subjectivity between 0.0 and 1.0. The sentence can be a string, Text, Sentence, ChunkWord or a Synset (see below). 

The positive() function returns True if the given sentence's polarity is above the threshold. The threshold can be lowered or raised, but overall +0.1 gives the best results for product reviews. Accuracy is about 75% for movie reviews.

sentiment(sentence)        # Returns a (polarity, subjectivity)-tuple.
positive(s, threshold=0.1) # Returns True if polarity >= threshold.
>>> from pattern.en import sentiment
>>> print sentiment(
>>>     "The movie attempts to be surreal by incorporating various time paradoxes,"
>>>     "but it's presented in such a ridiculous way it's seriously boring.") 

(-0.34, 1.0) 

In the example above, -0.34 is the average of surreal, various, ridiculous and seriously boring. To retrieve the scores for individual words, use the special assessments property, which yields a list of (words, polarity, subjectivity, label)-tuples.

>>> print sentiment('Wonderfully awful! :-)').assessments

[(['wonderfully', 'awful', '!'], -1.0, 1.0, None), 
 ([':-)'], 0.5, 1.0, 'mood')] 


Mood & modality

Grammatical mood refers to the use of auxiliary verbs (e.g., could, would) and adverbs (e.g., definitely, maybe) to express uncertainty. 

The mood() function returns either INDICATIVE, IMPERATIVE, CONDITIONAL or SUBJUNCTIVE for a given parsed Sentence. See the table below for an overview of moods.

The modality() function returns the degree of certainty as a value between -1.0 and +1.0, where values > +0.5 represent facts. For example, "I wish it would stop raining" scores -0.35, whereas "It will stop raining" scores +0.75. Accuracy is about 68% for Wikipedia texts.

modality(sentence) # Returns -1.0 => +1.0.
Mood Form Use Example
INDICATIVE none of the below  fact, belief It rains.
IMPERATIVE infinitive without to command, warning Don't rain!
CONDITIONAL would, could, should, may, or willcan + if conjecture It might rain.
SUBJUNCTIVE wish, were, or it is + infinitive wish, opinion I hope it rains.

For example:

>>> from pattern.en import parse, Sentence, parse
>>> from pattern.en import modality
>>> s = "Some amino acids tend to be acidic while others may be basic." # weaseling
>>> s = parse(s, lemmata=True)
>>> s = Sentence(s)
>>> print modality(s)




The pattern.en.wordnet module includes WordNet 3.0 and Oliver Steele's PyWordNet module. WordNet is a lexical database that groups related words into Synset objects (= sets of synonyms). Each synset provides a short definition and semantic relations to other synsets.

The synsets() function returns a list of Synset objects for a given word, where each set corresponds to a word sense (e.g., tree in the sense of plant, tree in the sense of diagram, etc.)

synset = wordnet.synsets(word, pos=NOUN)[i]
synset.pos                  # Part-of-speech: NOUN | VERB | ADJECTIVE | ADVERB.
synset.synonyms             # List of word forms (i.e., synonyms).
synset.gloss                # Definition string.
synset.lexname              # Category string, or None.
synset.ic                   # Information Content (float).
synset.antonym              # Synset (semantic opposite).
synset.hypernym             # Synset (semantic parent).
synset.hypernyms(recursive=False, depth=None)
synset.hyponyms(recursive=False, depth=None)
synset.meronyms()           # List of synsets (members/parts).
synset.holonyms()           # List of synsets (of which this is a member).
synset.similar()            # List of synsets (similar adjectives/verbs).
  • Synset.hypernyms() returns a list of  parent synsets (i.e., more general).
  • Synset.hyponyms() returns a list child synsets (i.e., more specific).
    With recursive=True, returns parents of parents or children of children.
    Optionally, returns parents or children recursively up to the given depth.

For example:

>>> from pattern.en import wordnet
>>> s = wordnet.synsets('bird')[0]
>>> print 'Definition:', s.gloss
>>> print '  Synonyms:', s.synonyms
>>> print ' Hypernyms:', s.hypernyms()
>>> print '  Hyponyms:', s.hyponyms()
>>> print '  Holonyms:', s.holonyms()
>>> print '  Meronyms:', s.meronyms()

Definition: u'warm-blooded egg-laying vertebrates characterized '
             'by feathers and forelimbs modified as wings'
  Synonyms: [u'bird']
 Hypernyms: [Synset(u'vertebrate')]
  Hyponyms: [Synset(u'cock'), Synset(u'hen'), ...]
  Holonyms: [Synset(u'Aves'), Synset(u'flock')]
  Meronyms: [Synset(u'beak'), Synset(u'feather'), ...]
Reference: Fellbaum, C. (1998). WordNet: An Electronic Lexical Database. Cambridge, MIT Press.

Synset similarity

The ancestor() function returns the common ancestor of two synsets. The similarity() function returns the semantic similarity of two synsets as a value between 0.01.0.

wordnet.ancestor(synset1, synset2)
wordnet.similarity(synset1, synset2)
>>> from pattern.en import wordnet
>>> a = wordnet.synsets('cat')[0]
>>> b = wordnet.synsets('dog')[0]
>>> c = wordnet.synsets('box')[0]
>>> print wordnet.ancestor(a, b)
>>> print wordnet.similarity(a, a) 
>>> print wordnet.similarity(a, b)
>>> print wordnet.similarity(a, c)  


Similarity is calculated using Lin's formula and Resnik's Information Content (IC). IC values for each synset are derived from the word count in Brown corpus.

lin = 2.0 * log(ancestor(synset1, synset2).ic) / log(synset1.ic * synset2.ic)

Synset sentiment

SentiWordNet is a lexical resource for opinion mining, with polarity and subjectivity scores for all WordNet synsets. SentiWordNet is free for non-commercial research purposes. To use SentiWordNet, request a download from the authors and put SentiWordNet*.txt in pattern/en/wordnet/. You can then use Synset.weight() in your script:

>>> from pattern.en import wordnet
>>> from pattern.en import ADJECTIVE
>>> print wordnet.synsets('happy', ADJECTIVE)[0].weight
>>> print wordnet.synsets('sad', ADJECTIVE)[0].weight

(0.375, 0.875)
(-0.625, 0.875)



The patten.en module includes a number of general-purpose word lists:

List Description Size Example
ACADEMIC English academic words 500 criterion, proportionally, research
BASIC English basic words 1,000 chicken, pain, road
PROFANITY English swear words 350  
TIME English time & date words 100 Christmas, past, saturday
>>> from pattern.en.wordlist import ACADEMIC
>>> words = open('paper.txt').read().split()
>>> words = [w for w in words if w not in ACADEMIC] 


See also

  • MBSP (GPL): robust parser using a memory-based learning approach, in Python.
  • NLTK (Apache): full natural language processing toolkit for Python.