Even after years of programming, I'm ashamed to say that I've never really fully grasped regular expressions. In general, when a problem calls for a regex, I can usually (after a bunch of referring to syntax) come up with an appropriate one, but it's a technique that I find myself using increasingly often.
So, to teach myself and understand regular expressions properly, I've decided to do what I always do when trying to learn something; i.e., try to write something ambitious that I'll probably abandon as soon as I feel I've learnt enough.
To this end, I want to write a regular expression parser in Python. In this case, "learn enough" means that I want to implement a parser that can understand Perl's extended regex syntax completely. However, it doesn't have to be the most efficient parser or even necessarily usable in the real-world. It merely has to correctly match or fail to match a pattern in a string.
The question is, where do I start? I know almost nothing about how regexes are parsed and interpreted apart from the fact that it involves a finite state automaton in some way. Any suggestions for how to approach this rather daunting problem would be much appreciated.
EDIT: I should clarify that while I'm going to implement the regex parser in Python, I'm not overly fussed about what programming language the examples or articles are written in. As long as it's not in Brainfuck, I will probably understand enough of it to make it worth my while.