def __init__(self, lemma=None):
"""Setup for DefaultLemmatizer().
:param lemma: String with default lemma to be assigned for all tokens;
set to None if no parameter is assigned.
"""
self._lemma = lemma
SequentialBackoffLemmatizer.__init__(self, None)
DefaultTagger.__init__(self, self._lemma)
def __init__(self, lemma=None):
"""Setup for DefaultLemmatizer().
:param lemma: String with default lemma to be assigned for all tokens;
set to None if no parameter is assigned.
"""
self._lemma = lemma
SequentialBackoffLemmatizer.__init__(self, None)
DefaultTagger.__init__(self, self._lemma)
def nltk_default_pos_tagger(input_dict):
"""
A tagger that assigns the same tag to every token.
>>> from nltk.tag.sequential import DefaultTagger
>>> default_tagger = DefaultTagger('NN')
>>> default_tagger.tag('This is a test'.split())
[('This', 'NN'), ('is', 'NN'), ('a', 'NN'), ('test', 'NN')]
This tagger is recommended as a backoff tagger, in cases where
a more powerful tagger is unable to assign a tag to the word
(e.g. because the word was not seen during training).
:param default_tag: The default tag "%(default)s". Set this to a different tag, such as "NN",
to change the default tag.
:returns pos_tagger: A python dictionary containing the POS tagger
object and its arguments.
"""
from nltk.tag import DefaultTagger
return {'pos_tagger': {
'function':'tag_sents',
'object': DefaultTagger(input_dict.get('default_tag','-None-'))
}
}
def unigram_bigram_tagger(train_sentences):
return BigramTagger(
train_sentences,
backoff=UnigramTagger(
train_sentences,
backoff=DefaultTagger("NN")
)
)
def nltk_brill_pos_tagger(input_dict):
"""Brill's transformational rule-based tagger. Brill taggers use an
initial tagger (such as ``tag.DefaultTagger``) to assign an initial
tag sequence to a text; and then apply an ordered list of
transformational rules to correct the tags of individual tokens.
These transformation rules are specified by the ``BrillRule``
interface.
Brill taggers can be created directly, from an initial tagger and
a list of transformational rules; but more often, Brill taggers
are created by learning rules from a training corpus, using either
``BrillTaggerTrainer`` or ``FastBrillTaggerTrainer``.
:param training_corpus: A tagged corpus consisting of a list of tagged
sentences, where each sentence is a list of (word, tag) tuples.
:param initial_tagger: The initial tagger. Brill taggers use an initial
tagger (such as ``DefaultTagger``) to assign an initial tag
sequence to a text.
:param max_rules: The maximum number of transformations to be created
:param min_score: The minimum acceptable net error reduction
that each transformation must produce in the corpus.
:param deterministic: If true, then choose between rules that
have the same score by picking the one whose __repr__
is lexicographically smaller. If false, then just pick the
first rule we find with a given score -- this will depend
on the order in which keys are returned from dictionaries,
and so may not be the same from one run to the next. If
not specified, treat as true iff trace > 0.
:param templates: templates to be used in training
:returns pos_tagger: A python dictionary containing the POS tagger
object and its arguments.
"""
training_corpus = corpus_reader(input_dict['training_corpus'])[:1000]
initial_tagger = input_dict['initial_tagger']['object'] if input_dict[
'initial_tagger'] else DefaultTagger('-None-')
max_rules = int(input_dict['max_rules']) #default 200
min_score = int(input_dict['min_score']) #default 2
deterministic = True
templates = getattr(nltk.tag.brill, input_dict['templates'])()
trainer = BrillTaggerTrainer(initial_tagger,
templates,
deterministic=deterministic,
trace=settings.DEBUG)
brill_tagger = trainer.train(
training_corpus, max_rules=max_rules,
min_score=min_score) #return BrillTagger(self._initial_tagger, rules)
if settings.DEBUG:
for rule in brill_tagger.rules():
print(str(rule))
return {'pos_tagger': {'function': 'tag_sents', 'object': brill_tagger}}
def nltk_classifier_based_pos_tagger(input_dict):
"""
A sequential tagger that uses a classifier to choose the tag for
each token in a sentence. The featureset input for the classifier
is generated by a feature detector function::
feature_detector(tokens, index, history) -> featureset
Where tokens is the list of unlabeled tokens in the sentence;
index is the index of the token for which feature detection
should be performed; and history is list of the tags for all
tokens before index.
Construct a new classifier-based sequential tagger.
:param training_corpus: A tagged corpus consisting of a list of tagged
sentences, where each sentence is a list of (word, tag) tuples.
:param backoff_tagger: A backoff tagger, to be used by the new tagger
if it encounters an unknown context.
TODO: odloci se katerega se obdrzi od naslednjih dveh
:param classifier_builder: A function used to train a new
classifier based on the data in *train*. It should take
one argument, a list of labeled featuresets (i.e.,
(featureset, label) tuples).
:param classifier: The classifier that should be used by the
tagger. #This is only useful if you want to manually
construct the classifier; normally, you would use *train*
instead.
:param backoff_tagger: A backoff tagger, used if this tagger is
unable to determine a tag for a given token.
:param cutoff_prob: If specified, then this tagger will fall
back on its backoff tagger if the probability of the most
likely tag is less than *cutoff_prob*.
:returns pos_tagger: A python dictionary containing the POS tagger
object and its arguments.
"""
#training_corpus=corpus_reader(input_dict['training_corpus']) #TODO: should it stay or should it go
backoff_tagger = input_dict['backoff_tagger']['object'] if input_dict[
'backoff_tagger'] else DefaultTagger('-None-')
classifier = None #(input_dict['classifier'])
cutoff_prob = int(
input_dict['cutoff_prob']) if input_dict['cutoff_prob'] else None
import nltk
tagger_object = ClassifierBasedPOSTagger(
train=nltk.corpus.brown.tagged_sents()[:5],
classifier=classifier,
backoff=backoff_tagger,
cutoff_prob=cutoff_prob)
return {'pos_tagger': {'function': 'tag_sents', 'object': tagger_object}}
def nltk_ngram_pos_tagger(input_dict):
"""
A tagger that chooses a token's tag based on its word string and
on the preceding n word's tags. In particular, a tuple
(tags[i-n:i-1], words[i]) is looked up in a table, and the
corresponding tag is returned. N-gram taggers are typically
trained on a tagged corpus.
Train a new NgramTagger using the given training data or
the supplied model. In particular, construct a new tagger
whose table maps from each context (tag[i-n:i-1], word[i])
to the most frequent tag for that context. But exclude any
contexts that are already tagged perfectly by the backoff
tagger.
:param training_corpus: A tagged corpus included with NLTK, such as treebank, brown, cess_esp, floresta,
or an Annotated Document Corpus in the standard TextFlows' adc format
:param backoff_tagger: A backoff tagger, to be used by the new
tagger if it encounters an unknown context.
:param cutoff: If the most likely tag for a context occurs
fewer than *cutoff* times, then exclude it from the
context-to-tag table for the new tagger.
:param n: N-gram is a contiguous sequence of n items from a given sequence of text or speech.
:returns pos_tagger: A python dictionary containing the POS tagger object and its arguments.
"""
training_corpus = corpus_reader(input_dict['training_corpus'])
backoff_tagger = input_dict['backoff_tagger']['object'] if input_dict[
'backoff_tagger'] else DefaultTagger('-None-')
n = int(input_dict['n']) #default 2
cutoff = int(input_dict['cutoff']) #default 0
return {
'pos_tagger': {
'function':
'tag_sents',
'object':
NgramTagger(n,
train=training_corpus,
model=None,
backoff=backoff_tagger,
cutoff=cutoff)
}
}
def nltk_affix_pos_tagger(input_dict):
"""
A tagger that chooses a token's tag based on a leading or trailing
substring of its word string. (It is important to note that these
substrings are not necessarily "true" morphological affixes). In
particular, a fixed-length substring of the word is looked up in a
table, and the corresponding tag is returned. Affix taggers are
typically constructed by training them on a tagged corpus.
:param training_corpus: A tagged corpus included with NLTK, such as treebank, brown, cess_esp, floresta,
or an Annotated Document Corpus in the standard TextFlows' adc format
:param backoff_tagger: A backoff tagger, to be used by the new
tagger if it encounters an unknown context.
:param affix_length: The length of the affixes that should be
considered during training and tagging. Use negative
numbers for suffixes.
:param min_stem_length: Any words whose length is less than
min_stem_length+abs(affix_length) will be assigned a
tag of None by this tagger.
:returns pos_tagger: A python dictionary containing the POS tagger object and its arguments.
"""
tagged_corpus = corpus_reader(input_dict['training_corpus'])
backoff_tagger = input_dict['backoff_tagger']['object'] if input_dict[
'backoff_tagger'] else DefaultTagger('-None-')
affix_length = int(input_dict['affix_length'])
min_stem_length = int(input_dict['min_stem_length'])
cutoff = int(input_dict['cutoff']) #default 0
return {
'pos_tagger': {
'function':
'tag_sents',
'object':
AffixTagger(tagged_corpus,
affix_length=affix_length,
cutoff=cutoff,
min_stem_length=min(min_stem_length, 2),
backoff=backoff_tagger)
}
}
def choose_lemma(self, tokens, index, history):
return DefaultTagger.choose_tag(self, tokens, index, history)
def choose_lemma(self, tokens, index, history):
return DefaultTagger.choose_tag(self, tokens, index, history)
