PHP is a scripting language similar to Python. If you're already familiar with Python, then almost all you need for PHP is a familiarity with its libraries. To really get something out of it also check out its magic methods.
Now normally PHP wouldn't be my first suggestion for someone looking for a language to learn as it tends to encourage people that don't know any better to write sloppy code . However, since you have a Python/Java background you shouldn't have such a problem since those languages tends to teach you proper OO coding techniques.
Furthermore PHP is very popular in the job market. I seriously doubt there are PHP developers out there starving. I can't guarantee however that such a job will be a good one since maintaining some of the legacy PHP code out there (especially PHP4) can be a mentally scarring experience. Not that you can't find horrible code in other languages, but you get the idea.
JSP on the other hand is basically Java with extra bits stuck on it. If you know Java, it's not a great leap to writting JSP. Of course Java is Java, so expect to spend a lot of time dealing with its formalities.