How regular expressions work in python ?

Question

I'm studying regular expressions in python 3 and I tried the following code :
https://code.sololearn.com/ccJb19pWb4n8/?ref=app
My problem is that I get an unexpected result. The objective is to obtain all the strings that match the pattern (ha){3,5).

Answer 1

You just need to change (ha) to (?:ha).

=> haRegex=re.compile(r'(?:ha){3,5}')

output:
['hahaha', 'hahahaha', 'hahahahaha', 'hahahahaha']

(ha) creates a capturing group and will always find/return "ha" and nothing else. (?:ha) is a non-capturing group. It allows you to use brackets (), followed by quantifiers like {3,5}, without creating a capturing group. It's difficult to explain, but once you get it, it makes sense.

Answer 2

Ahmed Errami It will match the last string too because 'hahahahahaha' (6 x ha) contains 'hahahahaha' (5 x ha).

If you don't want to include the last match, you can change the pattern to

haRegex=re.compile(r'\b(?:ha){3,5}\b')

\b marks a word boundary. Now it will only find whole "words" consisting of exactly 3 to 5 x ha: ['hahaha', 'hahahaha', 'hahahahaha'].

Answer 3

Thank you Anna. But I expect to get a list of only 3 elements because I have selected strings that contain 3 to 5 'ha' and they are 3.