Source code for textblob.base

# -*- coding: utf-8 -*-
"""Abstract base classes for models (taggers, noun phrase extractors, etc.)
which define the interface for descendant classes.

.. versionchanged:: 0.7.0
    All base classes are defined in the same module, ``textblob.base``.
"""
from __future__ import absolute_import
from abc import ABCMeta, abstractmethod

import nltk

from textblob.compat import with_metaclass

##### POS TAGGERS #####

class BaseTagger(with_metaclass(ABCMeta)):
    """Abstract tagger class from which all taggers
    inherit from. All descendants must implement a
    ``tag()`` method.
    """
    @abstractmethod
    def tag(self, text, tokenize=True):
        """Return a list of tuples of the form (word, tag)
        for a given set of text or BaseBlob instance.
        """
        return

##### NOUN PHRASE EXTRACTORS #####

class BaseNPExtractor(with_metaclass(ABCMeta)):
    """Abstract base class from which all NPExtractor classes inherit.
    Descendant classes must implement an ``extract(text)`` method
    that returns a list of noun phrases as strings.
    """

    @abstractmethod
    def extract(self, text):
        """Return a list of noun phrases (strings) for a body of text."""
        return

##### TOKENIZERS #####

class BaseTokenizer(with_metaclass(ABCMeta), nltk.tokenize.api.TokenizerI):
    """Abstract base class from which all Tokenizer classes inherit.
    Descendant classes must implement a ``tokenize(text)`` method
    that returns a list of noun phrases as strings.
    """
    @abstractmethod
    def tokenize(self, text):
        """Return a list of tokens (strings) for a body of text.

        :rtype: list
        """
        return

    def itokenize(self, text, *args, **kwargs):
        """Return a generator that generates tokens "on-demand".

        .. versionadded:: 0.6.0

        :rtype: generator
        """
        return (t for t in self.tokenize(text, *args, **kwargs))

##### SENTIMENT ANALYZERS ####


DISCRETE = 'ds'
CONTINUOUS = 'co'


class BaseSentimentAnalyzer(with_metaclass(ABCMeta)):
    """Abstract base class from which all sentiment analyzers inherit.
    Should implement an ``analyze(text)`` method which returns either the
    results of analysis.
    """
    kind = DISCRETE

    def __init__(self):
        self._trained = False

    def train(self):
        # Train me
        self._trained = True

    @abstractmethod
    def analyze(self, text):
        """Return the result of of analysis. Typically returns either a
        tuple, float, or dictionary.
        """
        # Lazily train the classifier
        if not self._trained:
            self.train()
        # Analyze text
        return None

##### PARSERS #####

class BaseParser(with_metaclass(ABCMeta)):
    """Abstract parser class from which all parsers inherit from. All
    descendants must implement a ``parse()`` method.
    """
    @abstractmethod
    def parse(self, text):
        """Parses the text."""
        return