Home/ Questions/Q 1061461
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-16T18:28:35+00:00

I get an error message when I use this expression: re.sub(r([^\s\w])(\s*\1)+,\\1,…) I checked the

  • 0

I get an error message when I use this expression:

re.sub(r"([^\s\w])(\s*\1)+","\\1","...")

I checked the regex at RegExr and it returns . as expected. But when I try it in Python I get this error message:

raise error, v # invalid expression
sre_constants.error: nothing to repeat

Can someone please explain?

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    It seems to be a python bug (that works perfectly in vim).
    The source of the problem is the (\s*…)+ bit. Basically , you can’t do (\s*)+ which make sense , because you are trying to repeat something which can be null.

    >>> re.compile(r"(\s*)+")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/System/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/re.py", line 180, in compile
    return _compile(pattern, flags)
  File "/System/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/re.py", line 233, in _compile
    raise error, v # invalid expression
sre_constants.error: nothing to repeat

    However (\s*\1) should not be null, but we know it only because we know what’s in \1. Apparently python doesn’t … that’s weird.

    • 0