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

[adang1345]

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

• gh-155254: Avoid warning about missing stdlib when using _pth files #156015
• [3.15] gh-155254: Avoid warning about missing stdlib when using _pth files (GH-156015) #156182

[picnixz]

cc @zooba

[StanFromIreland]

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. ;-)

[zooba]

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.

[zooba]

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