Python: Find URLs and add querystring pair

Question

I'm trying to affilliateize some legacy text in a Django webapp. It's a pretty simple scope. The text has some amazon URLs in and I want to munge my ?tag=xxx identifier onto the end of them.

I've written a template filter that I can quickly pass my text through but I'm slightly stuck on writing the regex logic.

t = text_from_template_engine
return re.sub(r'(https?://(?:www\.)?amazon\.co\.uk[\S]+)', r'\\\1?tag=xxx', t)

This seems to work on a very basic level but if the URL already has a querystring (as lots of organic Amazon URLs do by default), I would need an ampersand instead of a question mark.

There might be a quick way to detect two question marks and replace the second. I'm open to that suggestion.

What I'm really looking for is a regex-replace where I can pass the found string off to another method (in which I can detect existing question marks) that is expected to return the replacement string. Something like PHP's preg_replace_callback (et al). Does that exist?

Daniel Roseman · Accepted Answer · 2010-11-30 14:59:54Z

2

Yes, the second parameter to re.sub can be a function, which takes a match object and returns a string. See the documentation.

answered Nov 30, 2010 at 14:59

Daniel Roseman

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1 Comment

Oli Over a year ago

Mind... Blown... As usual, I need to RTFM ;)

Community · Accepted Answer · 2017-05-23 12:04:14Z

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Once you find the URL, you're better off parsing it properly rather than hacking it into a regex.

edited May 23, 2017 at 12:04

CommunityBot

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answered Nov 30, 2010 at 14:57

Ignacio Vazquez-Abrams

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Oli Over a year ago

Sure. But that's my problem. How do I find-and-replace in a way that lets me interfere in the middle?

Keng · Accepted Answer · 2010-11-30 15:09:15Z

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There might be a quick way to detect two question marks and replace the second. I'm open to that suggestion.

this will get the 2 question marks.

(\?|(\?\?))

I believe the non-passive group number for the double question mark will be $4 but you'll need to double check that and you can add back the single question mark in your replace.

edited Nov 30, 2010 at 15:09

answered Nov 30, 2010 at 14:57

Keng

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