Python regex replacement not working with group

Question

Trying to do the following: string = "2" replace to = "No 2"

using below regex in python:

re.sub(r'(.*)', r'No. \g<1>', '2')

But it returns:

'No. 2No. '

Can you please help what's going wrong?

Note: using 3.8.5 python version

CIsForCookies · Answer 1 · 2020-10-07T12:35:31.880

0

For me it works (maybe different python versions... I'm using 3.6.11 and it seems like 3.8's [which I assume OP is using] re works differently):

In [1]: import re

In [2]: re.sub(r'(.*)', r'No. \g<1>', '2')
Out[2]: 'No. 2'

But, I would suggest using a better regex:

In [3]: re.sub(r'(\d+)', r'No. \g<1>', '2')
Out[3]: 'No. 2'

This is better since it only catches the digits in the string:

In [4]: re.sub(r'(\d+)', r'No. \g<1>', '2 3 4 5 blabla')
Out[4]: 'No. 2 No. 3 No. 4 No. 5 blabla'

where your regex will just take the entire string:

In [5]: re.sub(r'(.*)', r'No. \g<1>', '2 3 4 5 blabla')
Out[5]: 'No. 2 3 4 5 blabla'

edited Oct 07 '20 at 12:35

answered Oct 07 '20 at 12:29

CIsForCookies

1

When I run his regex on python 3.8.5 it gives me his results. If I run it on 3.6.2 it gives the expected results. Yours works the same on both. – FrozenAra Oct 07 '20 at 12:33
1

@FrozenAra yeah, just tried it with 3.8.0 – CIsForCookies Oct 07 '20 at 12:34
Yes, i am using 3.8.5 – kailash19 Oct 07 '20 at 12:35
I recommend you to just use @ClsForCookies regex. I think regex behaviour changed with python 3.7 – FrozenAra Oct 07 '20 at 12:41
@FrozenAra Thing is the string could be anything, need to take everything. – kailash19 Oct 07 '20 at 13:03

1 Answers1