After spending an considerable amount of time installing MySQLdb on Mac OS X 10.5 Leopard, I had to repeat a similar exercise today. I am no expert at this kind of thing whatsoever. Still, I thought it might be useful to share my experiences with you.
I let Snow Leopard (NY Times review) in into my house last friday (August 28th, 2009) and the upgrade process (from Leopard) went really smoothly. Apart from a few programs not working anymore, most notably Cyberduck (which needed updating to a newer version), I did not notice any problems. The only worries I had about this update was my Django developer setup: Python, MySQL and some Python modules/libraries.
MySQL needs to be 64 bit
When I tested one of my Django projects, the first thing I noticed was that MySQL was not working properly anymore. I could not get MySQL to start from the PrefPane setting (under System Preferences). I turned out that Snow Leopard requires a 64 bit version of MySQL.
Solution: Download the 64 bit version of MySQL (there are Mac OS X packages (get the one for 10.5 - x86_64) on MySQL's website).
For more information see: Upgrading to Snow Leopard (Ruby on Rails) and Compiling MySQL on Snow Leopard - Hivelogic (if you like to go Pro).
The next "bump" in the road was MySQLdb. This Python DB API is needed to let Python (and Django) interact with MySQL properly. Since I installed (compiled) MySQLdb for the 32 bit version of MySQL, I had a hunch this one was not going to work anymore either. The first thing I tried was simple reinstalling MySQLdb (see Installing MySQLdb for more information). The installer was not too happy however and kept throwing error messages at me.
Solution: First, make sure you have the GCC compiler installed. You can install Xcode (Apple's developer software) for this. You can download this from Apple, but I remember spotting it on the Snow Leopard DVD (Optional Installs). However, it turned out that GCC has been updated by Apple and somehow my MySQLdb installer did not seem appreciate that. Eventually I got this working, but I am not even sure how. One possible solution might have been adding to my .bash_profile:
Adding the Mac OS X 10.4 option from the Xcode installer (from the DVD) was also a necessary step.
Now I finally got the MySQLdb install to complete. Unfortunately that did not change anything for me. From the message that MySQLdb reported when imported in the Python shell, I understood that it was still running the 32 bit version (seeing the i386 in the site-packages name of MySQLdb during the install, also alerted me to this).
I upgraded my Python installation on Leopard to Python 2.6.1 because I did not want to work with the older Python version that shipped with Leopard. Hopefully, I had assumed that Snow Leopard updated this Python installation (which was not the "System" installation) but it turned out that it did not. My Leopard installed Python was a 32 bit version and I suspected that this was the reason for me being still "stuck" with a broken setup.
Solution: I removed the $PATH settings from my .bash_profile so that the "Python" command would not point to the 32 bit Python anymore. After restarting the Terminal, Python referred to the "system" version of Python again (the one that shipped with Snow Leopard) and that was the 2.6.1 64 bit Python. With this Python I reinstalled MySQLdb, which now compiled to the 64 bit version. And it all worked!
I was not completely out of the woods yet because the Python installation I was now using did not have any of my other modules installed: Django, PIL, Django pagination, etc. Reinstalling those was not too hard though (download, unpack, "sudo python setup.py install").
Yes, there is a price to pay if you always want to run the newest and shiniest software. Especially if you do not always know exactly what you are doing (like me). Next year, with Mac OS X 10.7, we will see what happens again.