Additionally, the os module is supposed to closely follow the behaviour of the underlying operating system functions: https://docs.python.org/3/library/os.html  

> The design of all built-in operating system dependent modules of Python is such that as long as the same functionality is available, it uses the same interface; [..]

The POSIX symlimk function on which this is based has made the decision not to overwrite an existing symlink (See the EEXIST error in https://pubs.opengroup.org/onlinepubs/009695399/functions/symlink.html or man pages on symlink from one of the Linux distros: http://man7.org/linux/man-pages/man2/symlink.2.html )   As with many other POSIX-derived filesystem functions, the technique you propose, relying on atomic filesystem renames) would seem to be the standard method of writing race-resistant code.  Due to the mandate for the os module, it feels like that belongs in a utility function in custom code or another module rather than something for the os module.

A couple of thoughts on what you could do instead:

* A collection of utility functions that fixed race-conditions in filesystem handling could make a nice third party module on pypi.

* The stdlib shutil module provides an API that's supposed to be easier to implement common use cases than the os.* functions.  Perhaps you could propose your idea to the python-ideas mailing list as a new function in that module and see what people think of that?