数字和加号/减号的正则表达式

Question

My problem is that I can't figure out a way to define a regex that would print digits in case there is only +, -, [ or whitespace in front of them and only bracket or whitespace after. In addition if there is minus it should be printed. I have tried looking for similar cases and spent quite sometime with the problem but haven't been able to come up with an answer.

So what I have at the moment is:

\b([+-]?[0-9]+)\b

And it should print out 16, -55, and +18 from the following:

[16 ] [a44] [fg] [230+] [+-50] [ -55 ]x [+18]aff

At the moment it prints in addition 50 and 230 which it shouldn't. I would be grateful for any tips.

Answer 1

You may use

(?<![\w+-])[+-]?\d+(?![\w+-])

See the regex demo

Details

• (?<![\w+-]) - a negative lookbehind that fails the match if, immediately to the left of the current position, there is a word, - or + char
• [+-]? - an optional + or -
• \d+ - 1+ digits
• (?![\w+-]) - a negative lookahead that fails the match if, immediately to the right of the current position, there is a word, - or + char.

Python demo :

import re
rx = r"(?<![\w+-])[+-]?\d+(?![\w+-])"
s = "[16 ] [a44] [fg] [230+] [+-50] [ -55 ]x [+18]aff"
print( re.findall(rx, s) )
# => ['16', '-55', '+18']

Answer 2

Indeed \b matches any non-word character. + is a non-word character, so + in 230+ and + in +-50 match !