# Natural Language Toolkit: Tokenizer Utilities
#
# Copyright (C) 2001-2023 NLTK Project
# Author: Steven Bird <stevenbird1@gmail.com>
# URL: <https://www.nltk.org>
# For license information, see LICENSE.TXT
from re import finditer
from xml.sax.saxutils import escape, unescape
[docs]def string_span_tokenize(s, sep):
r"""
Return the offsets of the tokens in *s*, as a sequence of ``(start, end)``
tuples, by splitting the string at each occurrence of *sep*.
>>> from nltk.tokenize.util import string_span_tokenize
>>> s = '''Good muffins cost $3.88\nin New York. Please buy me
... two of them.\n\nThanks.'''
>>> list(string_span_tokenize(s, " ")) # doctest: +NORMALIZE_WHITESPACE
[(0, 4), (5, 12), (13, 17), (18, 26), (27, 30), (31, 36), (37, 37),
(38, 44), (45, 48), (49, 55), (56, 58), (59, 73)]
:param s: the string to be tokenized
:type s: str
:param sep: the token separator
:type sep: str
:rtype: iter(tuple(int, int))
"""
if len(sep) == 0:
raise ValueError("Token delimiter must not be empty")
left = 0
while True:
try:
right = s.index(sep, left)
if right != 0:
yield left, right
except ValueError:
if left != len(s):
yield left, len(s)
break
left = right + len(sep)
[docs]def regexp_span_tokenize(s, regexp):
r"""
Return the offsets of the tokens in *s*, as a sequence of ``(start, end)``
tuples, by splitting the string at each successive match of *regexp*.
>>> from nltk.tokenize.util import regexp_span_tokenize
>>> s = '''Good muffins cost $3.88\nin New York. Please buy me
... two of them.\n\nThanks.'''
>>> list(regexp_span_tokenize(s, r'\s')) # doctest: +NORMALIZE_WHITESPACE
[(0, 4), (5, 12), (13, 17), (18, 23), (24, 26), (27, 30), (31, 36),
(38, 44), (45, 48), (49, 51), (52, 55), (56, 58), (59, 64), (66, 73)]
:param s: the string to be tokenized
:type s: str
:param regexp: regular expression that matches token separators (must not be empty)
:type regexp: str
:rtype: iter(tuple(int, int))
"""
left = 0
for m in finditer(regexp, s):
right, next = m.span()
if right != left:
yield left, right
left = next
yield left, len(s)
[docs]def spans_to_relative(spans):
r"""
Return a sequence of relative spans, given a sequence of spans.
>>> from nltk.tokenize import WhitespaceTokenizer
>>> from nltk.tokenize.util import spans_to_relative
>>> s = '''Good muffins cost $3.88\nin New York. Please buy me
... two of them.\n\nThanks.'''
>>> list(spans_to_relative(WhitespaceTokenizer().span_tokenize(s))) # doctest: +NORMALIZE_WHITESPACE
[(0, 4), (1, 7), (1, 4), (1, 5), (1, 2), (1, 3), (1, 5), (2, 6),
(1, 3), (1, 2), (1, 3), (1, 2), (1, 5), (2, 7)]
:param spans: a sequence of (start, end) offsets of the tokens
:type spans: iter(tuple(int, int))
:rtype: iter(tuple(int, int))
"""
prev = 0
for left, right in spans:
yield left - prev, right - left
prev = right
[docs]class CJKChars:
"""
An object that enumerates the code points of the CJK characters as listed on
https://en.wikipedia.org/wiki/Basic_Multilingual_Plane#Basic_Multilingual_Plane
This is a Python port of the CJK code point enumerations of Moses tokenizer:
https://github.com/moses-smt/mosesdecoder/blob/master/scripts/tokenizer/detokenizer.perl#L309
"""
# Hangul Jamo (1100–11FF)
Hangul_Jamo = (4352, 4607) # (ord(u"\u1100"), ord(u"\u11ff"))
# CJK Radicals Supplement (2E80–2EFF)
# Kangxi Radicals (2F00–2FDF)
# Ideographic Description Characters (2FF0–2FFF)
# CJK Symbols and Punctuation (3000–303F)
# Hiragana (3040–309F)
# Katakana (30A0–30FF)
# Bopomofo (3100–312F)
# Hangul Compatibility Jamo (3130–318F)
# Kanbun (3190–319F)
# Bopomofo Extended (31A0–31BF)
# CJK Strokes (31C0–31EF)
# Katakana Phonetic Extensions (31F0–31FF)
# Enclosed CJK Letters and Months (3200–32FF)
# CJK Compatibility (3300–33FF)
# CJK Unified Ideographs Extension A (3400–4DBF)
# Yijing Hexagram Symbols (4DC0–4DFF)
# CJK Unified Ideographs (4E00–9FFF)
# Yi Syllables (A000–A48F)
# Yi Radicals (A490–A4CF)
CJK_Radicals = (11904, 42191) # (ord(u"\u2e80"), ord(u"\ua4cf"))
# Phags-pa (A840–A87F)
Phags_Pa = (43072, 43135) # (ord(u"\ua840"), ord(u"\ua87f"))
# Hangul Syllables (AC00–D7AF)
Hangul_Syllables = (44032, 55215) # (ord(u"\uAC00"), ord(u"\uD7AF"))
# CJK Compatibility Ideographs (F900–FAFF)
CJK_Compatibility_Ideographs = (63744, 64255) # (ord(u"\uF900"), ord(u"\uFAFF"))
# CJK Compatibility Forms (FE30–FE4F)
CJK_Compatibility_Forms = (65072, 65103) # (ord(u"\uFE30"), ord(u"\uFE4F"))
# Range U+FF65–FFDC encodes halfwidth forms, of Katakana and Hangul characters
Katakana_Hangul_Halfwidth = (65381, 65500) # (ord(u"\uFF65"), ord(u"\uFFDC"))
# Supplementary Ideographic Plane 20000–2FFFF
Supplementary_Ideographic_Plane = (
131072,
196607,
) # (ord(u"\U00020000"), ord(u"\U0002FFFF"))
ranges = [
Hangul_Jamo,
CJK_Radicals,
Phags_Pa,
Hangul_Syllables,
CJK_Compatibility_Ideographs,
CJK_Compatibility_Forms,
Katakana_Hangul_Halfwidth,
Supplementary_Ideographic_Plane,
]
[docs]def is_cjk(character):
"""
Python port of Moses' code to check for CJK character.
>>> CJKChars().ranges
[(4352, 4607), (11904, 42191), (43072, 43135), (44032, 55215), (63744, 64255), (65072, 65103), (65381, 65500), (131072, 196607)]
>>> is_cjk(u'\u33fe')
True
>>> is_cjk(u'\uFE5F')
False
:param character: The character that needs to be checked.
:type character: char
:return: bool
"""
return any(
[
start <= ord(character) <= end
for start, end in [
(4352, 4607),
(11904, 42191),
(43072, 43135),
(44032, 55215),
(63744, 64255),
(65072, 65103),
(65381, 65500),
(131072, 196607),
]
]
)
[docs]def xml_escape(text):
"""
This function transforms the input text into an "escaped" version suitable
for well-formed XML formatting.
Note that the default xml.sax.saxutils.escape() function don't escape
some characters that Moses does so we have to manually add them to the
entities dictionary.
>>> input_str = ''')| & < > ' " ] ['''
>>> expected_output = ''')| & < > ' " ] ['''
>>> escape(input_str) == expected_output
True
>>> xml_escape(input_str)
')| & < > ' " ] ['
:param text: The text that needs to be escaped.
:type text: str
:rtype: str
"""
return escape(
text,
entities={
r"'": r"'",
r'"': r""",
r"|": r"|",
r"[": r"[",
r"]": r"]",
},
)
[docs]def xml_unescape(text):
"""
This function transforms the "escaped" version suitable
for well-formed XML formatting into humanly-readable string.
Note that the default xml.sax.saxutils.unescape() function don't unescape
some characters that Moses does so we have to manually add them to the
entities dictionary.
>>> from xml.sax.saxutils import unescape
>>> s = ')| & < > ' " ] ['
>>> expected = ''')| & < > \' " ] ['''
>>> xml_unescape(s) == expected
True
:param text: The text that needs to be unescaped.
:type text: str
:rtype: str
"""
return unescape(
text,
entities={
r"'": r"'",
r""": r'"',
r"|": r"|",
r"[": r"[",
r"]": r"]",
},
)
[docs]def align_tokens(tokens, sentence):
"""
This module attempt to find the offsets of the tokens in *s*, as a sequence
of ``(start, end)`` tuples, given the tokens and also the source string.
>>> from nltk.tokenize import TreebankWordTokenizer
>>> from nltk.tokenize.util import align_tokens
>>> s = str("The plane, bound for St Petersburg, crashed in Egypt's "
... "Sinai desert just 23 minutes after take-off from Sharm el-Sheikh "
... "on Saturday.")
>>> tokens = TreebankWordTokenizer().tokenize(s)
>>> expected = [(0, 3), (4, 9), (9, 10), (11, 16), (17, 20), (21, 23),
... (24, 34), (34, 35), (36, 43), (44, 46), (47, 52), (52, 54),
... (55, 60), (61, 67), (68, 72), (73, 75), (76, 83), (84, 89),
... (90, 98), (99, 103), (104, 109), (110, 119), (120, 122),
... (123, 131), (131, 132)]
>>> output = list(align_tokens(tokens, s))
>>> len(tokens) == len(expected) == len(output) # Check that length of tokens and tuples are the same.
True
>>> expected == list(align_tokens(tokens, s)) # Check that the output is as expected.
True
>>> tokens == [s[start:end] for start, end in output] # Check that the slices of the string corresponds to the tokens.
True
:param tokens: The list of strings that are the result of tokenization
:type tokens: list(str)
:param sentence: The original string
:type sentence: str
:rtype: list(tuple(int,int))
"""
point = 0
offsets = []
for token in tokens:
try:
start = sentence.index(token, point)
except ValueError as e:
raise ValueError(f'substring "{token}" not found in "{sentence}"') from e
point = start + len(token)
offsets.append((start, point))
return offsets