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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"`PyMODINIT_FUNC` does not apply `__declspec(dllexport)` on Windows","articleBody":"The macro is [documented](https://docs.python.org/3/c-api/extension-modules.html#c.PyMODINIT_FUNC) as:\n\n\u003e Declare an extension module initialization function. This macro:\n\u003e * specifies the [PyObject](https://docs.python.org/3/c-api/structures.html#c.PyObject)* return type,\n\u003e * adds any special linkage declarations required by the platform, and\n\u003e * for C++, declares the function as extern \"C\".\n\nSpecifically, the special linkage declarations should be `__attribute__ ((visibility (\"default\")))` on GCC/clang, and `__declspec(dllexport)` on Windows.\nHowever, the definition assumes we're building CPython itself, and only adds a linkage declaration with `Py_ENABLE_SHARED` -- that is, when *Python itself* is built with a shared library.\n\n\nAccording to [MSVC docs](https://learn.microsoft.com/en-us/cpp/build/reference/export-exports-a-function?view=msvc-170):\n\n\u003e There are four methods for exporting a definition, listed in recommended order of use:\n\u003e 1. [`__declspec(dllexport)`](https://learn.microsoft.com/en-us/cpp/cpp/dllexport-dllimport?view=msvc-170) in the source code\n\u003e 2. An [EXPORTS](https://learn.microsoft.com/en-us/cpp/build/reference/exports?view=msvc-170) statement in a .def file\n\u003e 3. An /EXPORT specification in a LINK command\n\u003e 4. A [comment](https://learn.microsoft.com/en-us/cpp/preprocessor/comment-c-cpp?view=msvc-170) directive in the source code, of the form `#pragma comment(linker, \"/export: definition \")`.\n\nSetuptools, and historically distutils, [does (2)](https://github.com/pypa/setuptools/blob/d198e86f57231e83de87975c5c82bc40c196da79/setuptools/_distutils/compilers/C/msvc.py#L526) -- and so does, presumably, any other build system for native extensions on Windows.\nHowever, this breaks for modules that define the PEP-793 `PyModExport` hook.\n\nIt would be great to switch to the preferred (1), and then tell Setuptools to avoid `/EXPORT` for 3.15+.\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-141672\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/encukou","@type":"Person","name":"encukou"},"datePublished":"2025-11-17T16:42:36.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/141671/cpython/issues/141671"}