Regex to get character not between two other characters

Question

How would one use Regex to get a character/word that is not between two other characters/words?

For example, in:

hello world [hello hello] world hello [world hello world hello] world hello [hello] hello

It would select:

hello world [hello hello] world hello [world hello world hello] world hello [hello] hello

This question gets text, not between two characters ( (?<=^|\\])[^[]+ ), which is close, all one needs to do on top of that is select specific words from that.

Answer 1

You can take the opposite approach by selecting what you don't want, which is from an opening till closing square bracket. Then use an alternation using | and capture what you want to keep.

Using for exampole re.findall you get the values of the capturing groups, and then you can filter out the empty strings.

\[[^][]*]|\b(hello)\b

Regex demo | Python demo

Example code

import re
 
regex = r"\[[^][]*]|\b(hello)\b"
 
test_str = ("hello world [hello hello] world hello [world hello world hello] world hello [hello] hello")
 
print(list(filter(None, re.findall(regex, test_str))))

Output

['hello', 'hello', 'hello', 'hello']

Answer 2

Use PyPi regex:

import regex
text='hello world [hello hello] world hello [world hello world hello] world hello [hello] hello'
print( regex.sub(r'\[[^][]*](*SKIP)(?!)|\b(hello)\b', r'++\1++', text) )

Code demo

Output:

++hello++ world [hello hello] world ++hello++ [world hello world hello] world ++hello++ 
[hello] ++hello++

\\[[^][]*](*SKIP)(?!)|\\b(hello)\\ expression matches strings between square brackets and these matches are dropped, hello is matched within word boundaries and replaced eventually with regex.sub .