[ddj] Dynamic backreferences?

Wed Sep 25 23:50:04 UTC 2013

Hi,

Here is a python code that should do what you want

def colrepeat(text):
...     instr =  text.string[text.start()+1:text.end()-1]
...     outstr = '<'
...     for col in instr.split(','):
...             outstr = outstr + ','.join([col] * 3) + ','
...     outstr += '>'
...     return outstr
...
re.sub('\<[a-z\,]+\>', colrepeat, 'I like <red,green,blue> and
<white,black>')

On Wed, Sep 25, 2013 at 9:15 PM, Patrick Maynard <
patrickmaynard.bs at gmail.com> wrote:

> Is there a simple way to make a regular expression generate its own back
> references?
>
> For example, if I have strings "this is a <red,blue,green> set" and "this
> is a <red,brown,blue,green,brown> string" (and several other strings that
> vary in the number of color instances), and I know that the brackets will
> always be exclusively wrapped around the comma-delimited color list, can I
> write a single replacement pattern that will repeat each color three times
> before going to the next color?
>
> I realize that there are a ton of much better, non-big-hammer ways of
> doing this. I'm just curious about this as a sort of academic exercise at
> this point. Is there a way to accomplish this strictly with regex?
>
> -- Patrick
>
>
>
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-- 
Best Regards
Tarek Amr

http://tarekamr.appspot.com/
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