Regex: How to find substring that does NOT contain a certain word

Question

I have this string;

string = "STARTcandyFINISH  STARTsugarFINISH STARTpoisonFINISH STARTBlobpoisonFINISH STARTpoisonBlobFINISH"

I would like to match and capture all substrings that appear in between START and FINISH but only if the word "poison" does NOT appear in that substring. How do I exclude this word and capture only the desired substrings?

re.findall(r'START(.*?)FINISH', string)

Desired captured groups:

candy
sugar

@Sraw I'm not sure if this is a duplicate because my question is about avoiding a word - not just a single character (please correct me if I'm wrong - thank you) — etayluz, Jan 01 '20 at 08:57

score 1 · Accepted Answer · answered Jan 01 '20 at 07:18

Using a tempered dot, we can try:

string = "STARTcandyFINISH  STARTsugarFINISH STARTpoisonFINISH STARTBlobpoisonFINISH STARTpoisonBlobFINISH"
matches = re.findall(r'START((?:(?!poison).)*?)FINISH', string)
print(matches)

This prints:

['candy', 'sugar']

For an explanation of how the regex pattern works, we can have a closer look at:

(?:(?!poison).)*?

This uses a tempered dot trick. It will match, one character at a time, so long as what follows is not poison.

Regex: How to find substring that does NOT contain a certain word

1 Answers1