如何在一长串字符列表中识别regex坏字符？

Question

目标是将这个Perl regex (从这里)移植到Python中：

$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

也就是说。

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'))

但是当我试图编译regex时：

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

它抛出此错误：

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)

环顾四周，问题似乎是字符集中没有转义的破折号，Python正则表达式坏字符范围。。

看起来有一系列像破折号的符号在：

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

然后，我将破折号字符移到字符串的前面，但是还有更多的坏字符：

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

输出

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)

所以我把更多的角色移到前面：

>>> 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))

这似乎是一个没完没了的循环检测什么是“坏的字符范围”在一个正则表达式。

是否有一种方法可以自动识别正则表达式中的所有“坏字符”并将它们转移到前面？

Answer 1

这里的要点是，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- -而r'\\\g<0>'替换将用\和匹配值替换匹配值。