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.
If you're doing any multi threading development, pick Python over PHP.
From a coder's perspective, what kind of project should I choose python over php for where both could do the job?