Regural expression puzzle for gurus

[Alex Martelli]

"Pekka Niiranen" <krissepu at vip.fi> wrote in message
news:3B4EA0C8.9F697D06 at vip.fi...
> I have a string in the middle of a text starting with #-sign and ending
> to \W.
> I can find it with re.compile('#\w+') and  would like to replace it by
> adding a
> # -sign also to the end of it.
>
> Example:
>
>             original string:           xx:yy:#AAA.!:-#BBB:2324:#CCC:!"¤%
>
>             after replacement:    xx:yy:#AAA#.!:-#BBB#:2324:#CCC#:!"¤%
>
> How can I do replacement with a single regural expression line ?
>
> I have found a solution like:
>            text = 'xx:yy:#AAA:-#BBB:aa'
>            line = re.compile('#\w+')

line = re.compile('(#\w+)')
text = line.sub(r'\1#', text)

should do what you want.  The parentheses around the re's
pattern define a group, the \1 in sub backreferences to
the group (in many contexts "group 0" can be used to mean
the whole substring matched, but, I believe, not here, so
I don't think you can avoid the parentheses in the pattern).


Alex