After Apple rendered all my development tools (MacBook, iPad and iPod touch) obsolete and incompatible with iOS 6, I purchased a new MacBook Pro, running Lion. So I tried installing the software I've been using on the old MacBook to the new one.
One of that software is MySQLdb. Yet I didn't remember how I installed it in the first place. So I had to start from scratch. I'm a proponent of the principle "if it ain't broken don't fix it". Since Lion comes with Python 2.7 pre-installed, I figured I'd use that.
Next missing piece was MySQL. I used a .dmg from http://dev.mysql.com/downloads/mysql/, specifically mysql-5.1.63-osx10.6-x86_64.dmg. As the name indicates that's for a 64 bits architecture.
One important insight gathered from this site was that the architecture of Python, MySQL and the MySQLdb I've been trying to build should match. To check where I was standing I started the Python interpreter, made sure that MySQL server was running and used Activity Monitor to look at their processes like so:
So I clearly needed to build the 64 bits variant of MySQLdb. After downloading the sources from http://sourceforge.net/projects/mysql-python/ I followed the instructions from the README file with the following amendments:
1. Did a which mysql_config to see its location and updated the site.cfg to point there like so: mysql_config = /usr/local/mysql/bin/mysql_config
2. Instead python setup.py build did a ARCHFLAGS="-arch x86_64" python setup.py build.
3. Instead sudo python setup.py install I did sudo ARCHFLAGS="-arch x86_64" python setup.py install
To check the result I did import MySQLdb at the Python prompt and checked that no errors occur.
Note that following the step #2 you'll see a bunch of 'implicit conversion shortens 64-bit value into a 32-bit value' warnings. Those could probably be ignored, though there's a chance that some data loss may occur during those implicit conversions if the values on the right hand side of those assignments are large enough (probably unlikely). I tried a fix, to eliminate them, by using platform independent types like size_t instead of int and by matching the types of the variables in LHS return types of the functions in RHS of the assignments on the problematic lines. I placed a patch that attempts to fix those warnings at http://sourceforge.net/tracker/?func=detail&aid=3541063&group_id=22307&atid=374934.