Source code for nltk.tag.api

# Natural Language Toolkit: Tagger Interface
#
# Copyright (C) 2001-2021 NLTK Project
# Author: Edward Loper <edloper@gmail.com>
#         Steven Bird <stevenbird1@gmail.com> (minor additions)
#         Tom Aarsen <>
# URL: <https://www.nltk.org/>
# For license information, see LICENSE.TXT

"""
Interface for tagging each token in a sentence with supplementary
information, such as its part of speech.
"""
from abc import ABCMeta, abstractmethod
from functools import lru_cache
from itertools import chain
from typing import Dict

from nltk.internals import deprecated, overridden
from nltk.metrics import ConfusionMatrix, accuracy
from nltk.tag.util import untag


[docs]class TaggerI(metaclass=ABCMeta): """ A processing interface for assigning a tag to each token in a list. Tags are case sensitive strings that identify some property of each token, such as its part of speech or its sense. Some taggers require specific types for their tokens. This is generally indicated by the use of a sub-interface to ``TaggerI``. For example, featureset taggers, which are subclassed from ``FeaturesetTagger``, require that each token be a ``featureset``. Subclasses must define: - either ``tag()`` or ``tag_sents()`` (or both) """
[docs] @abstractmethod def tag(self, tokens): """ Determine the most appropriate tag sequence for the given token sequence, and return a corresponding list of tagged tokens. A tagged token is encoded as a tuple ``(token, tag)``. :rtype: list(tuple(str, str)) """ if overridden(self.tag_sents): return self.tag_sents([tokens])[0]
[docs] def tag_sents(self, sentences): """ Apply ``self.tag()`` to each element of *sentences*. I.e.:: return [self.tag(sent) for sent in sentences] """ return [self.tag(sent) for sent in sentences]
@deprecated("Use accuracy(gold) instead.") def evaluate(self, gold): return self.accuracy(gold)
[docs] def accuracy(self, gold): """ Score the accuracy of the tagger against the gold standard. Strip the tags from the gold standard text, retag it using the tagger, then compute the accuracy score. :param gold: The list of tagged sentences to score the tagger on. :type gold: list(list(tuple(str, str))) :rtype: float """ tagged_sents = self.tag_sents(untag(sent) for sent in gold) gold_tokens = list(chain.from_iterable(gold)) test_tokens = list(chain.from_iterable(tagged_sents)) return accuracy(gold_tokens, test_tokens)
@lru_cache(maxsize=1) def _confusion_cached(self, gold): """ Inner function used after ``gold`` is converted to a ``tuple(tuple(tuple(str, str)))``. That way, we can use caching on creating a ConfusionMatrix. :param gold: The list of tagged sentences to run the tagger with, also used as the reference values in the generated confusion matrix. :type gold: tuple(tuple(tuple(str, str))) :rtype: ConfusionMatrix """ tagged_sents = self.tag_sents(untag(sent) for sent in gold) gold_tokens = [token for _word, token in chain.from_iterable(gold)] test_tokens = [token for _word, token in chain.from_iterable(tagged_sents)] return ConfusionMatrix(gold_tokens, test_tokens)
[docs] def confusion(self, gold): """ Return a ConfusionMatrix with the tags from ``gold`` as the reference values, with the predictions from ``tag_sents`` as the predicted values. >>> from nltk.tag import PerceptronTagger >>> from nltk.corpus import treebank >>> tagger = PerceptronTagger() >>> gold_data = treebank.tagged_sents()[:10] >>> print(tagger.confusion(gold_data)) | - | | N | | O P | | N J J N N P P R R V V V V V W | | ' E C C D E I J J J M N N N O R P R B R T V B B B B B D ` | | ' , - . C D T X N J R S D N P S S P $ B R P O B D G N P Z T ` | -------+----------------------------------------------------------------------------------------------+ '' | <1> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . | , | .<15> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . | -NONE- | . . <.> . . 2 . . . 2 . . . 5 1 . . . . 2 . . . . . . . . . . . | . | . . .<10> . . . . . . . . . . . . . . . . . . . . . . . . . . . | CC | . . . . <1> . . . . . . . . . . . . . . . . . . . . . . . . . . | CD | . . . . . <5> . . . . . . . . . . . . . . . . . . . . . . . . . | DT | . . . . . .<20> . . . . . . . . . . . . . . . . . . . . . . . . | EX | . . . . . . . <1> . . . . . . . . . . . . . . . . . . . . . . . | IN | . . . . . . . .<22> . . . . . . . . . . 3 . . . . . . . . . . . | JJ | . . . . . . . . .<16> . . . . 1 . . . . 1 . . . . . . . . . . . | JJR | . . . . . . . . . . <.> . . . . . . . . . . . . . . . . . . . . | JJS | . . . . . . . . . . . <1> . . . . . . . . . . . . . . . . . . . | MD | . . . . . . . . . . . . <1> . . . . . . . . . . . . . . . . . . | NN | . . . . . . . . . . . . .<28> 1 1 . . . . . . . . . . . . . . . | NNP | . . . . . . . . . . . . . .<25> . . . . . . . . . . . . . . . . | NNS | . . . . . . . . . . . . . . .<19> . . . . . . . . . . . . . . . | POS | . . . . . . . . . . . . . . . . <1> . . . . . . . . . . . . . . | PRP | . . . . . . . . . . . . . . . . . <4> . . . . . . . . . . . . . | PRP$ | . . . . . . . . . . . . . . . . . . <2> . . . . . . . . . . . . | RB | . . . . . . . . . . . . . . . . . . . <4> . . . . . . . . . . . | RBR | . . . . . . . . . . 1 . . . . . . . . . <1> . . . . . . . . . . | RP | . . . . . . . . . . . . . . . . . . . . . <1> . . . . . . . . . | TO | . . . . . . . . . . . . . . . . . . . . . . <5> . . . . . . . . | VB | . . . . . . . . . . . . . . . . . . . . . . . <3> . . . . . . . | VBD | . . . . . . . . . . . . . 1 . . . . . . . . . . <6> . . . . . . | VBG | . . . . . . . . . . . . . 1 . . . . . . . . . . . <4> . . . . . | VBN | . . . . . . . . . . . . . . . . . . . . . . . . 1 . <4> . . . . | VBP | . . . . . . . . . . . . . . . . . . . . . . . . . . . <3> . . . | VBZ | . . . . . . . . . . . . . . . . . . . . . . . . . . . . <7> . . | WDT | . . . . . . . . 2 . . . . . . . . . . . . . . . . . . . . <.> . | `` | . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . <1>| -------+----------------------------------------------------------------------------------------------+ (row = reference; col = test) <BLANKLINE> :param gold: The list of tagged sentences to run the tagger with, also used as the reference values in the generated confusion matrix. :type gold: list(list(tuple(str, str))) :rtype: ConfusionMatrix """ return self._confusion_cached(tuple(tuple(sent) for sent in gold))
[docs] def recall(self, gold) -> Dict[str, float]: """ Compute the recall for each tag from ``gold`` or from running ``tag`` on the tokenized sentences from ``gold``. Then, return the dictionary with mappings from tag to recall. The recall is defined as: - *r* = true positive / (true positive + false positive) :param gold: The list of tagged sentences to score the tagger on. :type gold: list(list(tuple(str, str))) :return: A mapping from tags to recall :rtype: Dict[str, float] """ cm = self.confusion(gold) return {tag: cm.recall(tag) for tag in cm._values}
[docs] def precision(self, gold): """ Compute the precision for each tag from ``gold`` or from running ``tag`` on the tokenized sentences from ``gold``. Then, return the dictionary with mappings from tag to precision. The precision is defined as: - *p* = true positive / (true positive + false negative) :param gold: The list of tagged sentences to score the tagger on. :type gold: list(list(tuple(str, str))) :return: A mapping from tags to precision :rtype: Dict[str, float] """ cm = self.confusion(gold) return {tag: cm.precision(tag) for tag in cm._values}
[docs] def f_measure(self, gold, alpha=0.5): """ Compute the f-measure for each tag from ``gold`` or from running ``tag`` on the tokenized sentences from ``gold``. Then, return the dictionary with mappings from tag to f-measure. The f-measure is the harmonic mean of the ``precision`` and ``recall``, weighted by ``alpha``. In particular, given the precision *p* and recall *r* defined by: - *p* = true positive / (true positive + false negative) - *r* = true positive / (true positive + false positive) The f-measure is: - *1/(alpha/p + (1-alpha)/r)* With ``alpha = 0.5``, this reduces to: - *2pr / (p + r)* :param gold: The list of tagged sentences to score the tagger on. :type gold: list(list(tuple(str, str))) :param alpha: Ratio of the cost of false negative compared to false positives. Defaults to 0.5, where the costs are equal. :type alpha: float :return: A mapping from tags to precision :rtype: Dict[str, float] """ cm = self.confusion(gold) return {tag: cm.f_measure(tag, alpha) for tag in cm._values}
[docs] def evaluate_per_tag(self, gold, alpha=0.5, truncate=None, sort_by_count=False): """Tabulate the **recall**, **precision** and **f-measure** for each tag from ``gold`` or from running ``tag`` on the tokenized sentences from ``gold``. >>> from nltk.tag import PerceptronTagger >>> from nltk.corpus import treebank >>> tagger = PerceptronTagger() >>> gold_data = treebank.tagged_sents()[:10] >>> print(tagger.evaluate_per_tag(gold_data)) Tag | Prec. | Recall | F-measure -------+--------+--------+----------- '' | 1.0000 | 1.0000 | 1.0000 , | 1.0000 | 1.0000 | 1.0000 -NONE- | 0.0000 | 0.0000 | 0.0000 . | 1.0000 | 1.0000 | 1.0000 CC | 1.0000 | 1.0000 | 1.0000 CD | 0.7143 | 1.0000 | 0.8333 DT | 1.0000 | 1.0000 | 1.0000 EX | 1.0000 | 1.0000 | 1.0000 IN | 0.9167 | 0.8800 | 0.8980 JJ | 0.8889 | 0.8889 | 0.8889 JJR | 0.0000 | 0.0000 | 0.0000 JJS | 1.0000 | 1.0000 | 1.0000 MD | 1.0000 | 1.0000 | 1.0000 NN | 0.8000 | 0.9333 | 0.8615 NNP | 0.8929 | 1.0000 | 0.9434 NNS | 0.9500 | 1.0000 | 0.9744 POS | 1.0000 | 1.0000 | 1.0000 PRP | 1.0000 | 1.0000 | 1.0000 PRP$ | 1.0000 | 1.0000 | 1.0000 RB | 0.4000 | 1.0000 | 0.5714 RBR | 1.0000 | 0.5000 | 0.6667 RP | 1.0000 | 1.0000 | 1.0000 TO | 1.0000 | 1.0000 | 1.0000 VB | 1.0000 | 1.0000 | 1.0000 VBD | 0.8571 | 0.8571 | 0.8571 VBG | 1.0000 | 0.8000 | 0.8889 VBN | 1.0000 | 0.8000 | 0.8889 VBP | 1.0000 | 1.0000 | 1.0000 VBZ | 1.0000 | 1.0000 | 1.0000 WDT | 0.0000 | 0.0000 | 0.0000 `` | 1.0000 | 1.0000 | 1.0000 <BLANKLINE> :param gold: The list of tagged sentences to score the tagger on. :type gold: list(list(tuple(str, str))) :param alpha: Ratio of the cost of false negative compared to false positives, as used in the f-measure computation. Defaults to 0.5, where the costs are equal. :type alpha: float :param truncate: If specified, then only show the specified number of values. Any sorting (e.g., sort_by_count) will be performed before truncation. Defaults to None :type truncate: int, optional :param sort_by_count: Whether to sort the outputs on number of occurrences of that tag in the ``gold`` data, defaults to False :type sort_by_count: bool, optional :return: A tabulated recall, precision and f-measure string :rtype: str """ cm = self.confusion(gold) return cm.evaluate(alpha=alpha, truncate=truncate, sort_by_count=sort_by_count)
def _check_params(self, train, model): if (train and model) or (not train and not model): raise ValueError("Must specify either training data or trained model.")
[docs]class FeaturesetTaggerI(TaggerI): """ A tagger that requires tokens to be ``featuresets``. A featureset is a dictionary that maps from feature names to feature values. See ``nltk.classify`` for more information about features and featuresets. """