Windows embeddable distribution outputs WARN: Could not find the platform standard library directory!

Bug report

Bug description:

When the Windows embeddable distribution version 3.15.0rc1 is extracted and python.exe is run, a warning is shown.

WARN: Could not find the platform standard library directory! The Python 'home' directory was set to 'C:\\Users\\User\\Downloads\\python-3.15.0rc1-embed-amd64', is this correct?
Python 3.15.0rc1 (tags/v3.15.0rc1:37e98da, Aug  4 2026, 11:37:18) [MSC v.1951 64 bit (AMD64)] on win32
>>>

The warning first appears in 3.15.0a7. It is not present in 3.15.0a6 or 3.14.7. #145273 looks suspicious.

CPython versions tested on:

3.15

Operating systems tested on:

Windows

Linked PRs

@zooba

cc @zooba

I think it's a duplicate of #148750, based on Steve's comment there, but Windows things are scary so I'll leave this to someone else. ;-)

Yes, I think it's the same issue, and it's critical now because it's going to block PyManager updates (I expect python/pymanager#397 will fail in CI, as it's failing locally for me).

Still don't have time to look into it (I'm meant to be AFK and recovering right now), but will prioritise and block releases on this once I'm back online properly.

@chris-eibl

@chris-eibl found that this issue pre-dates #148750, so we should solve both, but they're likely independent.

Tagging this as a release blocker as well, since new extra/unnecessary output can be a major regression for users. But the fix (just disable the warning when the user has configured paths themselves) should be safe enough.

Debugging using

cpython/Modules/getpath.py

Line 29 in c5168ea

# warn(message) -- print a warning (if enabled)

shows that

cpython/Modules/getpath.py

Lines 777 to 779 in c5168ea

    
           elif not platstdlib_dir or not isdir(platstdlib_dir): 
        
               hint = home_hint if home else f'sys.exec_prefix is set to {exec_prefix}, is this correct?' 
        
               warn('WARN: Could not find the platform standard library directory! ' + hint)

fires because platstdlib_dir="<embedded-dir>\DLLs", which does not exist in the embedded case. IIUC, it is set here

cpython/Modules/getpath.py

Lines 740 to 741 in c5168ea

    
           if not platstdlib_dir and base_exec_prefix: 
        
               platstdlib_dir = joinpath(base_exec_prefix, PLATSTDLIB_LANDMARK)

where

cpython/Modules/getpath.py

Line 194 in c5168ea

PLATSTDLIB_LANDMARK = f'{platlibdir}'

and sys.platlibdir="DLLs". This has been the case for ages, but I wonder whether this should be an empty string in the embedded case?

The problem is that there's no "embedded case" - we only have one build, and the adaptation is dynamic.

Suppressing the warning when a ._pth file is used matches the same suppression when Py_SetPath or similar have been used, I think it was just missed.

gh-155254: Avoid warning about missing stdlib when using _pth files (G…

[3.15] gh-155254: Avoid warning about missing stdlib when using _pth …

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Windows embeddable distribution outputs `WARN: Could not find the platform standard library directory!` #155254

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	elif not platstdlib_dir or not isdir(platstdlib_dir):
	hint = home_hint if home else f'sys.exec_prefix is set to {exec_prefix}, is this correct?'
	warn('WARN: Could not find the platform standard library directory! ' + hint)

	if not platstdlib_dir and base_exec_prefix:
	platstdlib_dir = joinpath(base_exec_prefix, PLATSTDLIB_LANDMARK)

Windows embeddable distribution outputs WARN: Could not find the platform standard library directory! #155254

Description

Bug report

Bug description:

CPython versions tested on:

Operating systems tested on:

Linked PRs

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picnixz commented on Aug 5, 2026

StanFromIreland commented on Aug 5, 2026

zooba commented on Aug 11, 2026

zooba commented on Aug 17, 2026

zooba commented on Aug 18, 2026

chris-eibl commented on Aug 18, 2026

zooba commented on Aug 18, 2026

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Windows embeddable distribution outputs `WARN: Could not find the platform standard library directory!` #155254