I was in the same situation about six months ago. I studied the Pylons and then delved into the reddit code. For example, the model code was extremely secret (spread over one hundred files), and it seemed that simple changes would be a difficult task, at best the documents were scarce. Maintaining with the trunk seemed impossible. There was one guy with a little time who could answer questions briefly since he left.
It was obvious that I was completely alone. After a month or two from nowhere, I decided to look for other options. It looked interesting:
However, I preferred working in Python with PHP, so I explored creating my own in Django. A few months later, in my free time, I have about 50% of the things I need from reddit, and I understand every line of code in the code base. If I had to do it again, I would save this time and build my first for the first time. If there was something built for work, I would take it, but I am not dissatisfied with this path, since it gives me exactly what I need.
Remember that you can still remove a module or two from reddit. For example, a code for sorting comments (standard algorithm) at your leisure.
While on this, I also looked at Pinax, a Django distribution with network tidbits already installed. It interested me, but clouds hung above it, it seemed that there was too little community, and contributions dried up. Now it seems dead.
ps Learn some Postgres, it is not much different from other databases and is much more powerful on average, well-documented, and the price is right.