The py.exe launcher, when used interactively, no longer prefers Python 2 over Python 3 when the user doesn’t specify a version (via command line arguments or a config file). Handling of shebang lines remains unchanged - “python” refers to Python 2 in that case.
python.exe and pythonw.exe have been marked as long-path aware, which means that when the 260 character path limit may no longer apply. See removing the MAX_PATH limitation for details.
A sys.path file can be added to force isolated mode and fully specify all search paths to avoid registry and environment lookup. Seethe documentation for more information.