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GeezerVison is showing github.com — GH-124241: try reading `/proc/self/exe` to determine `sys.executable` by FFY00 · Pull Request #145486 · python/cpython

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@FFY00

@FFY00 FFY00 commented Mar 3, 2026 •
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$ bash -c "exec -a echo $(pwd)/python -c 'import sys; print(sys.executable)'"
/home/anubis/git/cpython/python
  • Issue: sys.executable is sometimes wrong #124241

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@FFY00
pythonGH-124241: try reading /proc/self/exe to determine sys.executable
6ecb062 
Signed-off-by: Filipe Laíns <[email protected]>
@bedevere-app bedevere-app Bot mentioned this pull request Mar 3, 2026
sys.executable is sometimes wrong #124241
Open
@bedevere-app bedevere-app Bot added the awaiting core review label Mar 3, 2026
FFY00
FFY00 commented Mar 3, 2026
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Comment thread Modules/getpath.py Resolved

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vstinner
vstinner reviewed Mar 4, 2026
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Comment thread Modules/getpath.py Outdated
if not executable and os_name == 'posix':
# On Linux, try resolving the executable path via procfs
try:
executable = realpath('/proc/self/exe')

@vstinner vstinner Mar 4, 2026

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realpath() returns /proc/self/exe unmodified if it cannot resolve the symlink. I would prefer using readlink() here. But it requires more work, since Modules/getpath.c doesn't implement it here. I can help implementing readlink() in getpath.c if you want.

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@FFY00 FFY00 Mar 4, 2026

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Right, using readlink would also be my preference, I just went for this implementation for simplicity. We could move this to progname_to_dict (computes real_executable), but we should still try to honor program_name if it points to the same path.

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FFY00 added 3 commits March 4, 2026 18:24
@FFY00
Use readlink to read /proc/self/exe
065bed6 
Signed-off-by: Filipe Laíns <[email protected]>
@FFY00
Add missing real_executable check
74c5658 
Signed-off-by: Filipe Laíns <[email protected]>
@FFY00
Add test_bad_argv0_posix
e9b4131 
Signed-off-by: Filipe Laíns <[email protected]>
@FFY00
FFY00 requested a review from vstinner March 4, 2026 18:38
@FFY00
Don't set real_executable if readlink returns an empty string
b70fd54 
Signed-off-by: Filipe Laíns <[email protected]>
@FFY00

FFY00 commented Mar 4, 2026

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Well, this is kind of messy. It seems that several tests rely on being able to feed real_executable a fake path. Since this is then used to search for the standard library directories, we cannot easily modify the behavior without causing breakage for some embedding users.

I'm gonna see if I can find a way to do this without breaking the module path calculation.
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@gpshead

gpshead commented Apr 11, 2026

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Indeed. sys.executable cannot be assumed to exist or simply be set to /proc/self/exe -> 's symlink target for such reasons.

There may be no meaningful executable, and the actual executed binary if it even exists on a filesystem that /proc/self/exe can point to, does not have to be a Python interpreter or behave like one.

It is common to see two behaviors in embedding scenarios, either sys.executable = None or something like sys.executable = "/<non-existant-path and explanation>" made up by the embedder such that any code which tries to use the string winds up with an explanation of what's wrong in the error message. Especially when the embedder has fully embedded the standard library in a hermetic executable manner.
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@gpshead
gpshead marked this pull request as draft April 11, 2026 21:48
@bedevere-app bedevere-app Bot removed the awaiting core review label Apr 11, 2026
@github-actions

github-actions Bot commented May 17, 2026

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This PR is stale because it has been open for 30 days with no activity.
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@github-actions github-actions Bot added the stale Stale PR or inactive for long period of time. label May 17, 2026
@Lekensteyn Lekensteyn mentioned this pull request Jul 19, 2026
sys.executable can be a relative path contrary to documented behavior [3.11 regression] #154160
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@FFY00 @gpshead @vstinner
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