I've done what you are saying, after several years of high end PHP development. But it was not exactly a simple switch. We develop enterprise-grade software, so it was worthwhile to make the switch.
I suggest you spend a good deal of time working with some python frameworks. Much will depend on your skill as a web-programmer and general-programmer.
PHP is a web-programming language that just kind of works out of the box. Python is a general purpose programming language (which works out of the box for general programming), but in order to use it for web-development, you must have several different components working together.
I suggest you get Apache + mod_wsgi working first. DO NOT try to compile them -- get an operating system (Fedora, ubuntu) that has packages out of the box.
Put together a couple of simple WSGI scripts in python to see how it works.
Then start with a really simple framework (like bottle or flask) to take it to the next level.
Go from there. Good luck!