I've never used python before. I've used php for about 5 years now. I plan to learn python, but I'm not sure what for yet. If I can think of a project that might be better to do in python, I'll use that to learn it.
Edit: just to add this as an important note, I do mean strictly for linux, not multi-platform.
Edit 2: I'm hoping for objective answers, like a specific project, not a general field of projects, etc.
A project you want to maintain over any length of time.
I've had to maintain PHP code and there is something about the fact that you can mix HTML and code that makes PHP stuff a nightmare.
Python has a much higher level of abstraction and makes more maintainable code much easier to write and much more importantly for maintenance - read.
All IMHO of course as this is a rather subjective question.
From a coder's perspective, what kind of project should I choose python over php for where both could do the job?