Write your own!
For some apps which have a certain level of complexity and require some extra flexibility, you end up wasting more time fighting the framework than getting the job done.
It helps if you have a well defined standard in place, for python, that means WSGI. Coupled with good libraries, it's hard to beat.
Maybe you end up writing a couple scripts to tie them together or something, but it's hardly a framework. And in many cases, yes, it is a better choice than a framework. And still a better choice than writing your own framework.
Basically, I'm saying if you're using a language which has mature frameworks and/or mature libraries which could be forged into an ad-hoc framework (templating, serving, ORM, etc.) it is terrible advise to tell people "just write your own".
Only in the case that you've considered all existing (relevant) options and determined none of them meet your use case (and none can be minimally altered to do so) should you consider writing your own. Anything else is a waste of time and effort.
But Im' still not happy :) I'm sure a lot of popular frameworks were created without any necessity, simply because they were fun to make. Some turned out to have qualities that nobody (including its creator) would have been able to spell out beforehand.