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.
Anything that requires background processing or any significant amount of code that doesn't just show a user a page.  Python is really good as a scripting language, and writing a command line Python script is commonplace; writing a PHP script to do command line work is rare.
From a coder's perspective, what kind of project should I choose python over php for where both could do the job?