Python: Does mkstemp open files only if they don't already exist?

Question

I assume the answer is "Yes", but is it safe to expect that tempfile.mkstemp() will only create a file that doesn't already exist? I presume that there's no chance of it over-writing an existing file (say, due to a race-condition).

Answer 1

It depends on OS support, but with that, yes, it is guaranteed to be safe; the file is opened with an exclusivity flag. Check your system's man pages for details, or here:

http://linux.die.net/man/3/open

O_EXCL|O_CREATE makes an "atomic file creation" operation which will fail if another process is doing the same thing. I'm not sure how mkstemp() handles that failure, but my guess/expectation is that it would pick a different file name and try again.