Python 正则表达式 - 替换所有出现的未以特定字符开头的关键字

Question

Problem
I'm trying to replace all occurrences of keyword not preceded by # or [[ with [[keyword]] .

For instance, the strings

keyword
#keyword
some keyword
[[keyword]] keyword

would be replaced with

[[keyword]]
#keyword
some [[keyword]]
[[keyword]] [[keyword]]

Attempt
I've tried ^(?!#.*$)keyword which does not work when keyword has at least one other word in front of it.

Removing the ^ however causes all occurrences of keyword to be replaced, including the ones directly after a pound sign and brackets.

Question
How can I replace all occurrences of keyword except when following a # or [[ ?

Answer 1

You can use

\b(?<!\[\[)(?<!#)keyword\b

See the regex demo . Details :

• \\b - a word boundary
• (?<!\\[\\[) - no [[ substring is allowed immediately on the left
• (?<!#) - no # char is allowed immediately on the left
• keyword - a string
• \\b - word boundary.

See the Python demo :

import re
text = "keyword\n#keyword\nsome keyword\n[[keyword]] keyword"
print( re.sub(r'\b(?<!\[\[)(?<!#)keyword\b', r'[[\g<0>]]', text) )
## => [[keyword]]
## => #keyword
## => some [[keyword]]
## => [[keyword]] [[keyword]]

Note the [[\\g<0>]] replacement contains a backreference to the whole match, \\g<0> . You may want to use \\1 if you add capturing parentheses around keyword in the regex pattern.