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# Natural Language Toolkit: Tokenizer Interface
#
# Copyright (C) 2001-2019 NLTK Project
# Author: Edward Loper <edloper@gmail.com>
# Steven Bird <stevenbird1@gmail.com>
# URL: <http://nltk.org/>
# For license information, see LICENSE.TXT
"""
Tokenizer Interface
"""
from abc import ABCMeta, abstractmethod
from six import add_metaclass
from nltk.internals import overridden
from nltk.tokenize.util import string_span_tokenize
@add_metaclass(ABCMeta)
class TokenizerI(object):
"""
A processing interface for tokenizing a string.
Subclasses must define ``tokenize()`` or ``tokenize_sents()`` (or both).
"""
@abstractmethod
def tokenize(self, s):
"""
Return a tokenized copy of *s*.
:rtype: list of str
"""
if overridden(self.tokenize_sents):
return self.tokenize_sents([s])[0]
def span_tokenize(self, s):
"""
Identify the tokens using integer offsets ``(start_i, end_i)``,
where ``s[start_i:end_i]`` is the corresponding token.
:rtype: iter(tuple(int, int))
"""
raise NotImplementedError()
def tokenize_sents(self, strings):
"""
Apply ``self.tokenize()`` to each element of ``strings``. I.e.:
return [self.tokenize(s) for s in strings]
:rtype: list(list(str))
"""
return [self.tokenize(s) for s in strings]
def span_tokenize_sents(self, strings):
"""
Apply ``self.span_tokenize()`` to each element of ``strings``. I.e.:
return [self.span_tokenize(s) for s in strings]
:rtype: iter(list(tuple(int, int)))
"""
for s in strings:
yield list(self.span_tokenize(s))
class StringTokenizer(TokenizerI):
"""A tokenizer that divides a string into substrings by splitting
on the specified string (defined in subclasses).
"""
def tokenize(self, s):
return s.split(self._string)
def span_tokenize(self, s):
for span in string_span_tokenize(s, self._string):
yield span