如何识别一长串字符中的正则表达式坏字符？

Question

目标是将这个 Perl 正则表达式（来自 here）移植到 Python：

$norm_text =~ s/(\P{N})(\p{P})/$1 $2 /g;

首先我将\p{P} 和\P{N} 字符数组复制到一个可读的文本文件中：

• Number.txt
• Punctuation.txt

即

import requests
from six import text_type

n_url = 'https://raw.githubusercontent.com/alvations/charguana/master/charguana/data/perluniprops/Number.txt'
p_url = 'https://raw.githubusercontent.com/alvations/charguana/master/charguana/data/perluniprops/Punctuation.txt'

NUMS = text_type(requests.get(n_url).content.decode('utf8'))
PUNCTS = text_type(requests.get(p_url).content.decode('utf8'))

但是当我尝试编译正则表达式时：

re.compile(u'([{n}])([{p}])'.format(n=NUMS, p=PUNCTS)

它会抛出这个错误：

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/alvas/anaconda3/lib/python3.6/re.py", line 233, in compile
    return _compile(pattern, flags)
  File "/Users/alvas/anaconda3/lib/python3.6/re.py", line 301, in _compile
    p = sre_compile.compile(pattern, flags)
  File "/Users/alvas/anaconda3/lib/python3.6/sre_compile.py", line 562, in compile
    p = sre_parse.parse(p, flags)
  File "/Users/alvas/anaconda3/lib/python3.6/sre_parse.py", line 856, in parse
    p = _parse_sub(source, pattern, flags & SRE_FLAG_VERBOSE, False)
  File "/Users/alvas/anaconda3/lib/python3.6/sre_parse.py", line 415, in _parse_sub
    itemsappend(_parse(source, state, verbose))
  File "/Users/alvas/anaconda3/lib/python3.6/sre_parse.py", line 763, in _parse
    p = _parse_sub(source, state, sub_verbose)
  File "/Users/alvas/anaconda3/lib/python3.6/sre_parse.py", line 415, in _parse_sub
    itemsappend(_parse(source, state, verbose))
  File "/Users/alvas/anaconda3/lib/python3.6/sre_parse.py", line 552, in _parse
    raise source.error(msg, len(this) + 1 + len(that))
sre_constants.error: bad character range ~-- at position 217 (line 1, column 218)

环顾问题似乎是字符集中没有转义的破折号Python regex bad character range.。

看起来有一系列类似破折号的符号：

>>> NUMS[215:352]
'~----------------------------------------------------------------------------------------------------------------------------------------'

然后我将破折号字符移到字符串的前面，但还有更多坏字符：

>>> NUMS2 = re.escape(NUMS[215:352]) + NUMS[:215] + NUMS[352:]
>>> re.compile(u'([{n}])'.format(n=NUMS2))

[出]：

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/alvas/anaconda3/lib/python3.6/re.py", line 233, in compile
    return _compile(pattern, flags)
  File "/Users/alvas/anaconda3/lib/python3.6/re.py", line 301, in _compile
    p = sre_compile.compile(pattern, flags)
  File "/Users/alvas/anaconda3/lib/python3.6/sre_compile.py", line 562, in compile
    p = sre_parse.parse(p, flags)
  File "/Users/alvas/anaconda3/lib/python3.6/sre_parse.py", line 856, in parse
    p = _parse_sub(source, pattern, flags & SRE_FLAG_VERBOSE, False)
  File "/Users/alvas/anaconda3/lib/python3.6/sre_parse.py", line 415, in _parse_sub
    itemsappend(_parse(source, state, verbose))
  File "/Users/alvas/anaconda3/lib/python3.6/sre_parse.py", line 763, in _parse
    p = _parse_sub(source, state, sub_verbose)
  File "/Users/alvas/anaconda3/lib/python3.6/sre_parse.py", line 415, in _parse_sub
    itemsappend(_parse(source, state, verbose))
  File "/Users/alvas/anaconda3/lib/python3.6/sre_parse.py", line 552, in _parse
    raise source.error(msg, len(this) + 1 + len(that))
sre_constants.error: bad character range ¬-- at position 502 (line 1, column 503)

所以我把更多的字符移到了前面：

>>> NUMS2 = re.escape(NUMS[215:352]) + NUMS[:215] + NUMS[352:]
>>> NUMS3 = re.escape(NUMS2[500:504]) + NUMS2[:500] + NUMS2[504:]
>>> re.compile(u'([{n}])'.format(n=NUMS3))

这似乎是检测正则表达式中“错误字符范围”的无限循环。

有没有办法自动识别正则表达式中的所有“坏字符”并将它们移到前面？

Answer 1

这里的重点是您需要在字符类中转义^、-、] 和\ 字符。

使用

NUMS = re.sub(r'[]^\\-]', r'\\\g<0>', NUMS)
PUNCTS = re.sub(r'[]^\\-]', r'\\\g<0>', PUNCTS)
rx = re.compile(u'([{n}])([{p}])'.format(n=NUMS, p=PUNCTS)

r'[]^\\-]' 模式将匹配 1 个字符 - ]、^、\ 或 - - 和 r'\\\g<0>' 替换将用 \ 和匹配值替换匹配值。