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GeezerVison is showing github.com — gh-85470: Delay load ole32.dll in the _ctypes module by serhiy-storchaka · Pull Request #155435 · python/cpython

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@serhiy-storchaka

@serhiy-storchaka serhiy-storchaka commented Aug 9, 2026 •
edited by bedevere-app Bot
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Measured on Windows 11 with a debug x64 build -- import _ctypes before the change loads user32.dll, ole32.dll, gdi32.dll, win32u.dll and combase.dll; after it, only combase.dll remains (pulled in by oleaut32, which does not depend on user32). A plain python.exe already loaded none of them, so ctypes was the last thing making the interpreter a GUI process -- and it is the module a console script needs in order to call SetConsoleCtrlHandler() in the first place.

ProgIDFromCLSID() in SetComError() is the only ole32 use in _ctypes, and it is reached only when formatting an error from a COM interface method. PCbuild/_wmi.vcxproj already delay loads the same DLL.

test_ctypes passes (679 tests). This covers the PCbuild build only; resolving ProgIDFromCLSID() through GetProcAddress() would also cover other toolchains, at the cost of some C code.

  • Issue: [ctypes] Enable handling logoff and shutdown Windows console events #85470

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@serhiy-storchaka
pythongh-85470: Delay load ole32.dll in the _ctypes module
ab4d315 
ole32.dll pulls in user32.dll, which makes the system treat the process as
a GUI process and stop sending logoff and shutdown console control events
to it.  It is only needed for ProgIDFromCLSID() when formatting a COM error.
@serhiy-storchaka
serhiy-storchaka requested a review from a team as a code owner August 9, 2026 13:52
@serhiy-storchaka
serhiy-storchaka requested review from eryksun and zooba August 9, 2026 13:53
@bedevere-app bedevere-app Bot mentioned this pull request Aug 9, 2026
[ctypes] Enable handling logoff and shutdown Windows console events #85470
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@bedevere-app bedevere-app Bot added the awaiting core review label Aug 9, 2026
@serhiy-storchaka

serhiy-storchaka commented Aug 9, 2026

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Verified the actual effect, not just the module list: two processes started from the same build in the same interactive session, one of them force-loading user32.dll to emulate the previous state, each with a SetConsoleCtrlHandler() installed through ctypes. On logoff the process without user32.dll received CTRL_LOGOFF_EVENT and ran its handler; the one with user32.dll loaded was terminated without any event.
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@serhiy-storchaka
serhiy-storchaka merged commit 0e8100a into python:main Aug 29, 2026
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@bedevere-app bedevere-app Bot removed the awaiting core review label Aug 29, 2026
@serhiy-storchaka
serhiy-storchaka deleted the gh-85470-ctypes-delayload-ole32 branch August 29, 2026 18:04
clin1234 pushed a commit to clin1234/cpython that referenced this pull request Sep 12, 2026
@serhiy-storchaka @clin1234
pythongh-85470: Delay load ole32.dll in the _ctypes module (pythonGH-…
e2eb95f 
…155435)

ole32.dll pulls in user32.dll, which makes the system treat the process as
a GUI process and stop sending logoff and shutdown console control events
to it.  It is only needed for ProgIDFromCLSID() when formatting a COM error.
This was referenced Oct 8, 2026
Windows: import hashlib loads user32.dll and the GDI DLLs through libcrypto; delay-load user32 #159008
Open
gh-159008: Delay load user32.dll in libcrypto on Windows #159009
Closed
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@eryksun eryksun Awaiting requested review from eryksun
@zooba zooba Awaiting requested review from zooba

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@serhiy-storchaka
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