CODEWITHSUNDEEP
pythonregexstring
saroele
saroele

Reputation: 10099

How to modify this string in Python

I have a string in which I need to add a '\' in front of every '[' or ']', except if the brackets enclose an x like this: '[x]'. In the other cases, the brackets will always enclose a number.

Example: 'Foo[123].bar[x]' should become 'Foo\[123\].bar[x]'.

What is the best way to achieve this? Thanks a lot on beforehand.

Upvotes: 1

Views: 161

Answers (3)

FailedDev
FailedDev

Reputation: 26930

A different approach, just put a slash before [] only if they aren't followed by x] or preceded by [x .

result = re.sub(r"(\[(?!x\])|(?<!\[x)\])", r"\\\1", subject)

Explanation:

# (\[(?!x\])|(?<!\[x)\])
# 
# Match the regular expression below and capture its match into backreference number 1 «(\[(?!x\])|(?<!\[x)\])»
# Match either the regular expression below (attempting the next alternative only if this one fails) «\[(?!x\])»
# Match the character “[” literally «\[»
# Assert that it is impossible to match the regex below starting at this position (negative lookahead) «(?!x\])»
# Match the character “x” literally «x»
# Match the character “]” literally «\]»
# Or match regular expression number 2 below (the entire group fails if this one fails to match) «(?<!\[x)\]»
# Assert that it is impossible to match the regex below with the match ending at this position (negative lookbehind) «(?<!\[x)»
# Match the character “[” literally «\[»
# Match the character “x” literally «x»
# Match the character “]” literally «\]»

Upvotes: 0

cmh
cmh

Reputation: 10927

You can do it without reaching for regexs like this:

s.replace('[', '\[').replace(']', '\]').replace('\[x\]', '[x]')

Upvotes: 6

g.d.d.c
g.d.d.c

Reputation: 47978

Something like this ought to work:

>>> import re
>>>
>>> re.sub(r'\[(\d+)\]', r'\[\1\]', 'Foo[123].bar[x]')
'Foo\\[123\\].bar[x]'

Upvotes: 8

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