Regex/Python: Substitution in Python when the Regex already do the substitution

Question

I'm trying to remove duplicate lines with this regex that works great:

(.*+)\n*(\1\n+)*

But when I try to use it in Python it doesn't work:

response1 = re.sub(r'(.*+)\n*', r'(\1\n+)*', response1)

Error:

Exception has occurred: re.error
multiple repeat at position 3

Am I doing something wrong?

Thank you,

Possible duplicate of [Alternative to possessive quantifier in python](https://stackoverflow.com/questions/44458122/alternative-to-possessive-quantifier-in-python) — CertainPerformance, Jan 09 '19 at 03:13
You could also use `[^\n]` instead of `.` to achieve the same effect — CertainPerformance, Jan 09 '19 at 03:15
I don't have a problem with quantifiers nor the Regex itself, I'm trying to make it work in Python — Creek Barbara, Jan 09 '19 at 03:16
The possessive quantifier *is* the problem - native Python doesn't support them. — CertainPerformance, Jan 09 '19 at 03:16
I'm trying to understand the post you've sent, but I've no idea what it's talking about. I'm new to Python and Rege unfortunately. — Creek Barbara, Jan 09 '19 at 03:21
Remove the possessive quantifier and use `[^\n]` instead of `.`. Also, the replacement string should just be the replacement string (possibly with ``\`` groups), not a regular expression. — CertainPerformance, Jan 09 '19 at 03:22

user2468968 · Accepted Answer · 2019-01-09T03:31:03.917

1

The "multiple repeat at position 3" problem is with the regex:

.*+

You can use either ".*" or ".+". Something like the following should remove consecutive duplicated lines:

response = """A
A    
A
B
B
A
A
"""
print(re.sub(r'(.*\n)(\1)+', r'\2', response))

Output

A
B
A

edited Jan 09 '19 at 03:31

answered Jan 09 '19 at 03:24

user2468968

I used your code and got this error: expected string or bytes-like object – Creek Barbara Jan 09 '19 at 03:26
Likely 'response' is not a string. What is 'response' – user2468968 Jan 09 '19 at 03:27

1 Answers1