Don't - by mistake - call one of your files the same as a module you will be loading. For example random.py is a bad idea if you will import random. Your code will try to locate random.py to load, but will find itself and not the one that comes with Python.
Python will also create a random.pyc file - a compiled file - and it will take time till you recall this and delete that too. Till then the whole thing will seem to be broken.