Rename file without overwriting existing files

[Jon Ribbens]

On 2017-01-30, Jussi Piitulainen <jussi.piitulainen at helsinki.fi> wrote:
> It doesn't seem to be documented. I looked at help(os.link) on Python
> 3.4 and the corresponding current library documentation on the web. I
> saw no mention of what happens when dst exists already.
>
> Also, creating a hard link doesn't seem to work between different file
> systems, which may well be relevant to Steve's case. I get:
>
>     OSError: [Errno 18] Invalid cross-device link: [snip]
>
> And that also is not mentioned in the docs.

Nor *should* either of those things be mentioned in the Python docs.

A lot of the functions of the 'os' module do nothing but call the
underlying OS system call with the same name. It would not only be
redundant to copy the OS documentation into the Python documentation,
it would be misleading and wrong, because of course the behaviour may
vary slightly from OS to OS.