Rename file without overwriting existing files

Mon Jan 30 08:58:10 EST 2017

Jussi Piitulainen wrote:
> Peter Otten writes:
>>> Steve D'Aprano wrote:

>>> The wider context is that I'm taking from 1 to <arbitrarily huge number>
>>> path names to existing files as arguments, and for each path name I
>>> transfer the file name part (but not the directory part) and then rename
>>> the file. For example:
>>>>>> foo/bar/baz/spam.txt
>>>>>> may be renamed to:
>>>>>> foo/bar/baz/ham.txt
>>>>>> but only provided ham.txt doesn't already exist.
>>>> Google finds
>>>> http://stackoverflow.com/questions/3222341/how-to-rename-without-race-conditions
>>>> and from a quick test it appears to work on Linux:
>> It doesn't seem to be documented. 

For functions with a C equivalent a look into the man page is usually 
helpful.
> 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.

In his example above he operates inside a single directory. Can one 
directory spread across multiple file systems?
> I get:
>> OSError: [Errno 18] Invalid cross-device link: [snip]
>> And that also is not mentioned in the docs.