Releases for recent security vulnerability

Hi all,

How come a description of how to exploit a security vulnerability
comes before a release for said vulnerability? I'm talking about this:
http://blog.python.org/2011/04/urllib-security-vulnerabil...

My understanding is that the whole point of asking people not to
report security vulnerability publicly was to allow time to release a
fix.

If developers haven't had enough time to release the fix, that's fine.
But I can't think of a sensible reason why it should be announced
first.

Cheers,

 - Gustavo.