I don't know much about writing operating systems, but I though this would be a good way to learn. There are tutorials for raspberry pi operating systems, but they're not linux-based or made with python. I'm just looking for a general tutorial here.
Operating systems generally use "low level" languages like c/c++/d in order to have proper access to system resources.  The problems with writing one in python are first, you need something to run an interpreter below it (defeating the purpose of having the OS be written in python) and second, there aren't good ways to manage resources in python.  Furthermore, you said you want it to be linux based, however, linux is written in c (for the reasons listed above and a few more) and therefore writing something in python will not be very productive.  If you want to stick with python, maybe you could write a window manager for linux instead?  It would be much easier than an OS and python would be a fine language for such a project.
Programming a linux-based Raspberry Pi operating system with python