I'm looking for some relatively simple, well-written object-oriented code to learn from. I'm a beginner.
So far I have looked at WordPress and Serendipity. WordPress is huge and Serendipity is not object-oriented. To make things worse, both still support PHP4.
Any recommendations? Thanks!
Assuming you want to stick with PHP, Drupal is very object oriented - and with the upcoming Drupal 7 release is becoming more so. I believe Drupal 7 is going to be PHP5 only, so it's using some of the features.
Not sure it qualifies for your needs though, as it's rather large ... that said, the Module based approach means that the system is already broken down into discrete blocks of functionality, which would make it much easier to get your head around.
Alternatively, if appropriate for your learning style, grab a copy of "Object Thinking" from Microsoft Press. It's language agnostic and really really good at covering the concepts in a way thats both understandable and easy to apply.
If you're interested in learning about a basic, object oriented blog setup, try installing Pylons and follow the Simple Site tutorial in the Pylons book. It walks you through all the basics of setting up a blog in an incremental fashion and has a lot of discussion about the details you might otherwise gloss over if you're just reading through a massive project.
Joomla! is also a good option. It's fairly large, but it's definitely manageable and shows you a lot of what you can do with OO PHP
It's also more of a CMS than blogging engine, but some of the principals are similar.
Good luck!