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gh-141671: PyMODINIT_FUNC: apply __declspec(dllexport) on Windows #141672

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gh-141671: PyMODINIT_FUNC: apply __declspec(dllexport) on Windows #141672

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39d18d1
gh-141671: Use __declspec(dllexport) when not building core
encukou Nov 17, 2025
ad9110c
blurb
encukou Nov 17, 2025
fd34aff
Use _PyINIT_EXPORTED_SYMBOL
encukou Nov 18, 2025
c0e0a83
Use `__declspec(dllexport)` outside core
encukou Nov 18, 2025
5abc323
Allow embedders to customize
encukou Nov 18, 2025
82ad329
Remove duplication with defaults
encukou Nov 18, 2025
35a088a
Remove duplication with default
encukou Nov 18, 2025
b39a5a8
Reduce diff
encukou Nov 18, 2025
13da2c0
Merge in the main branch
encukou Dec 16, 2025
5091b79
Link macro that's now documented
encukou Dec 16, 2025
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31 changes: 16 additions & 15 deletions Include/exports.h
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,12 @@
#define Py_EXPORTED_SYMBOL
#define Py_LOCAL_SYMBOL
#endif
/* module init functions outside the core must be exported */
#if defined(Py_BUILD_CORE)
#define _PyINIT_EXPORTED_SYMBOL Py_EXPORTED_SYMBOL
#else
#define _PyINIT_EXPORTED_SYMBOL __declspec(dllexport)
#endif
#else
/*
* If we only ever used gcc >= 5, we could use __has_attribute(visibility)
Expand All @@ -52,19 +58,16 @@
#define Py_EXPORTED_SYMBOL
#define Py_LOCAL_SYMBOL
#endif
#define _PyINIT_EXPORTED_SYMBOL Py_EXPORTED_SYMBOL
#endif

/* only get special linkage if built as shared or platform is Cygwin */
#if defined(Py_ENABLE_SHARED) || defined(__CYGWIN__)
# if defined(HAVE_DECLSPEC_DLL)
# if defined(Py_BUILD_CORE) && !defined(Py_BUILD_CORE_MODULE)
# define PyAPI_FUNC(RTYPE) Py_EXPORTED_SYMBOL RTYPE
# define PyAPI_DATA(RTYPE) extern Py_EXPORTED_SYMBOL RTYPE
/* module init functions inside the core need no external linkage */
/* except for Cygwin to handle embedding */
# if defined(__CYGWIN__)
# define _PyINIT_FUNC_DECLSPEC Py_EXPORTED_SYMBOL
# else /* __CYGWIN__ */
# if !defined(__CYGWIN__)
# define _PyINIT_FUNC_DECLSPEC
# endif /* __CYGWIN__ */
# else /* Py_BUILD_CORE */
Expand All @@ -77,12 +80,6 @@
# define PyAPI_FUNC(RTYPE) Py_IMPORTED_SYMBOL RTYPE
# endif /* !__CYGWIN__ */
# define PyAPI_DATA(RTYPE) extern Py_IMPORTED_SYMBOL RTYPE
/* module init functions outside the core must be exported */
# if defined(__cplusplus)
# define _PyINIT_FUNC_DECLSPEC extern "C" Py_EXPORTED_SYMBOL
# else /* __cplusplus */
# define _PyINIT_FUNC_DECLSPEC Py_EXPORTED_SYMBOL
# endif /* __cplusplus */
# endif /* Py_BUILD_CORE */
# endif /* HAVE_DECLSPEC_DLL */
#endif /* Py_ENABLE_SHARED */
Expand All @@ -96,13 +93,17 @@
#endif
#ifndef _PyINIT_FUNC_DECLSPEC
# if defined(__cplusplus)
# define _PyINIT_FUNC_DECLSPEC extern "C" Py_EXPORTED_SYMBOL
# define _PyINIT_FUNC_DECLSPEC extern "C" _PyINIT_EXPORTED_SYMBOL
# else /* __cplusplus */
# define _PyINIT_FUNC_DECLSPEC Py_EXPORTED_SYMBOL
# define _PyINIT_FUNC_DECLSPEC _PyINIT_EXPORTED_SYMBOL
# endif /* __cplusplus */
#endif

#define PyMODINIT_FUNC _PyINIT_FUNC_DECLSPEC PyObject*
#define PyMODEXPORT_FUNC _PyINIT_FUNC_DECLSPEC PyModuleDef_Slot*
#ifndef PyMODINIT_FUNC
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@vstinner vstinner Dec 17, 2025

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Supporting an already defined PyMODINIT_FUNC/PyMODEXPORT_FUNC is a new feature. Is it really worth it? I'm not against it, just curious.

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@encukou encukou Dec 17, 2025

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It's an escape hatch: if there's an unexpected problem with this PR, this can allow people to hotfix it without patching or waiting for a new release.

#define PyMODINIT_FUNC _PyINIT_FUNC_DECLSPEC PyObject*
#endif
#ifndef PyMODEXPORT_FUNC
#define PyMODEXPORT_FUNC _PyINIT_FUNC_DECLSPEC PyModuleDef_Slot*
#endif

#endif /* Py_EXPORTS_H */
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/C_API/2025-11-17-17-46-16.gh-issue-141671.cVXNW5.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
:c:macro:`PyMODINIT_FUNC` (and the new :c:macro:`PyMODEXPORT_FUNC`) now adds
a linkage declaration (``__declspec(dllexport)``) on Windows.
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