realpath has a race condition which might cause it to throw spurious exceptions

[bitonic]

Bug report

realpath tests if a file is a symlink using islink, which just returns False if the file does not exist. But then uses readlink a bit later to test the source of the link, which throws an exception if the file does not exists. If the file is a symlink and is deleted between islink and readlink, we get a spurious exception.

This reproduces the error using code copy-pasted from Python 3.9: https://gist.github.com/bitonic/e0977aaa674523a9ffe0e77a96cd6cc7 .

Your environment

• CPython 3.9
• ArchLinux x86_64

[sobolevn]

I can reproduce this on 3.12 as well.

[sobolevn]

Removing 3.9, because it only receives security fixes.
(this might have some security implications, but this needs further investigation)