Python scripts are text files containing Python source code, which is run using the Python interpreter (the .py extension is one way for Windows to detect that the script should be run using the Python interpreter). Once you have a DRM-free MOBI file, then mobi2lrf (another Python script, part of calibre, which was formally known as libprs500) is one way to convert it. See
Question about libprs500 and DRM-PRC files.... If you have calibre installed, mobi2lrf (not mobi2lrf.py) will be in your "path" and can be run from a command window in any directory.