forwards-compatibility

What pre-engineering do you do to ensure data compatibility for future versions of your app?

I am doing some significant refactoring and feature-adding on a project, and have just broken backwards compatibility with my data. I did it by creating a bunch of subclasses from the class that I used to house my data in, and loading in old serialized objects no longer works.. What kind of pre-engineering or strategies do you employ to...

What version of Python should I be using to develop web applications?

Currently I have python 3.1.1 installed on my system, same version on my server with WSGI 3.0 running on Apache 2.2. I want to keep using python 3.1, but I'm finding that lots of libraries/frameworks don't support it yet, namely Django, Pylons, MySQLdb, etc. I also checked an account I have on a friend's server, and it is running pytho...