为字符串中的所有非单词字符添加反斜杠[重复]

Question

由于我想将列表 (url_key) 中字符串的每个元素作为正则表达式来识别另一个列表中的元素是否具有模式，因此我需要为每个元素的所有非单词字符添加反斜杠在url_key 中使用python。

我的代码示例：

import re
sentences = ["Disallow DCCP sockets due to such NFC-3456",
            "Check at http://www.n.io/search?query=title++sub/file.html",
            "Specifies the hash algorithm on them"]

url_key = ['www.n.io/search?query=title++sub', 'someweb.org/dirs.io']    # there are thousands of elements
add_key = ['NFC-[0-9]{4}', 'CEZ-[0-9a-z]{4,8}']    # there are hundreds of elements

pattern = url_key + add_key
mykey = re.compile('(?:% s)' % '|'.join(pattern))

for item in sentences:
    if mykey.search(item):
        print (item, ' --> Keyword is found')
    else:
        print (item, ' --> Keyword is not Found')

但是这段代码给了我一个错误：

error                             Traceback (most recent call last)
<ipython-input-80-5348ee9c65ec> in <module>()
      8 
      9 pattern = url_key + add_key
---> 10 mykey = re.compile('(?:% s)' % '|'.join(pattern))
     11 
     12 for item in sentences:

~/anaconda3/lib/python3.6/re.py in compile(pattern, flags)
    231 def compile(pattern, flags=0):
    232     "Compile a regular expression pattern, returning a pattern object."
--> 233     return _compile(pattern, flags)
    234 
    235 def purge():

~/anaconda3/lib/python3.6/re.py in _compile(pattern, flags)
    299     if not sre_compile.isstring(pattern):
    300         raise TypeError("first argument must be string or compiled pattern")
--> 301     p = sre_compile.compile(pattern, flags)
    302     if not (flags & DEBUG):
    303         if len(_cache) >= _MAXCACHE:

~/anaconda3/lib/python3.6/sre_compile.py in compile(p, flags)
    560     if isstring(p):
    561         pattern = p
--> 562         p = sre_parse.parse(p, flags)
    563     else:
    564         pattern = None

~/anaconda3/lib/python3.6/sre_parse.py in parse(str, flags, pattern)
    853 
    854     try:
--> 855         p = _parse_sub(source, pattern, flags & SRE_FLAG_VERBOSE, 0)
    856     except Verbose:
    857         # the VERBOSE flag was switched on inside the pattern.  to be

~/anaconda3/lib/python3.6/sre_parse.py in _parse_sub(source, state, verbose, nested)
    414     while True:
    415         itemsappend(_parse(source, state, verbose, nested + 1,
--> 416                            not nested and not items))
    417         if not sourcematch("|"):
    418             break

~/anaconda3/lib/python3.6/sre_parse.py in _parse(source, state, verbose, nested, first)
    763                 sub_verbose = ((verbose or (add_flags & SRE_FLAG_VERBOSE)) and
    764                                not (del_flags & SRE_FLAG_VERBOSE))
--> 765                 p = _parse_sub(source, state, sub_verbose, nested + 1)
    766             if not source.match(")"):
    767                 raise source.error("missing ), unterminated subpattern",

~/anaconda3/lib/python3.6/sre_parse.py in _parse_sub(source, state, verbose, nested)
    414     while True:
    415         itemsappend(_parse(source, state, verbose, nested + 1,
--> 416                            not nested and not items))
    417         if not sourcematch("|"):
    418             break

~/anaconda3/lib/python3.6/sre_parse.py in _parse(source, state, verbose, nested, first)
    617             if item[0][0] in _REPEATCODES:
    618                 raise source.error("multiple repeat",
--> 619                                    source.tell() - here + len(this))
    620             if sourcematch("?"):
    621                 subpattern[-1] = (MIN_REPEAT, (min, max, item))

error: multiple repeat at position 31

预期结果：

Disallow DCCP sockets due to such NFC-3456 --> Keyword is found 
Check at http://www.n.io/search?query=title++sub/file.html --> Keyword is found
Specifies the hash algorithm on them --> Keyword is not found

任何帮助将不胜感激。谢谢。

Answer 1

您应该使用原始字符串：

result = re.sub('(\W)', r'\\\1', mystring)

或转义反斜杠：

result = re.sub('(\W)', '\\\\\\1', mystring)

Answer 2

您的主要问题是字符串转义在正则表达式替换转义之前生效。切换到原始字符串（以禁止字符串转义）并转义反斜杠（因为\\ 本身就是替换转义）将解决此问题：

>>> print(re.sub(r'(\W)', r'\\\1', '?:n.io/search?query=title++sub'))
\?\:n\.io\/search\?query\=title\+\+sub

请注意，您可能不需要如此广泛的转义。如果您只想转义正则表达式特殊字符，re.escape 将为您执行此操作：

>>> print(re.escape('?:n.io/search?query=title++sub'))
\?:n\.io/search\?query=title\+\+sub

不添加不必要的转义符（不需要对正则表达式字符进行去特殊化的转义符）。