os.path.realpath() RecursionError

[jwilk]

os.path.realpath() attempts to detect symlink loops, but this is not bulletproof;
it's possible to make it fall into infinite recursion.

Reproducer:

import os
import tempfile

with tempfile.TemporaryDirectory() as tmpdir:
    os.chdir(tmpdir)
    os.symlink('../' * (1 + tmpdir.count('/')) + f'{tmpdir}/d', 'd')
    os.path.realpath('d')

Traceback:

Traceback (most recent call last):
  File ".../recursiverealpath.py", line 7, in <module>
    os.path.realpath('d')
  File "<frozen posixpath>", line 427, in realpath
  File "<frozen posixpath>", line 487, in _joinrealpath
  File "<frozen posixpath>", line 487, in _joinrealpath
  File "<frozen posixpath>", line 487, in _joinrealpath
  [Previous line repeated 993 more times]
  File "<frozen posixpath>", line 442, in _joinrealpath
  File "<frozen posixpath>", line 63, in isabs
RecursionError: maximum recursion depth exceeded

Tested with Python 3.12.8.

[keainye]

This issue no longer reproduces in the the latest version (Python 3.14.0a3+ (heads/main:f802c8bf87, Jan 7 2025, 08:12:30) [GCC 12.2.0] on linux).

And in my opinion it seems to be an issue with os.symlink as it doesn't handle illegal paths...

[jwilk]

This issue no longer reproduces in the the latest version

Looks like this was indeed fixed in abfa16b ("GH-114847: Speed up posixpath.realpath() (#114848)").

in my opinion it seems to be an issue with os.symlink as it doesn't handle illegal paths...

No, os.symlink() works as expected.

[picnixz]

@barneygale Should we backport gh-114848 to fix the issue or is there something else we should do for 3.12 and 3.13?

[barneygale]

I think #114848 landed in 3.13 already? Not sure about backporting to 3.12 - it's close to EOL and the fix is invasive

[picnixz]

Ok, yes indeed it landed in 3.13.0a6. I think we can close this one as wont fix for 3.12 and completed for 3.13+.