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C API: Enable limited C API tests on Free Threading #155561
Description
Currently, the _testlimitedcapi extension module is not built with the limited C API on Free Threading which is misleading and defeats the purpose of this extension.
PEP 803 added Py_TARGET_ABI3T macro to Python 3.15 which makes it possible to build a C extension using the limited C API when using Free Threading. So I propose building _testlimitedcapi using Py_TARGET_ABI3T to test properly the limited C API on Free Threading.
One limitation is that Py_TARGET_ABI3T minimum version is Python 3.15, whereas _testlimitedcapi/<file>.c files target older Python versions. Anyway, we have to only define Py_TARGET_ABI3T on Free Threading, or define Py_LIMITED_API macro otherwise (build with GIL). Example:
#include "pyconfig.h" // Py_GIL_DISABLED
#ifdef Py_GIL_DISABLED
# define Py_TARGET_ABI3T 0x030f0000
#else
// Need limited C API version 3.13 for Py_GetConstant()
# define Py_LIMITED_API 0x030d0000
#endif
Activity
gh-155561: Build most _testlimitedcapi files with Py_TARGET_ABI3T (#1…
pythongh-155561: Use PySlot API in Modules/_testlimitedcapi.c
pythongh-155561: Build most _testlimitedcapi files with Py_TARGET_ABI…
gh-155561: Use multi-phase init for Modules/_testlimitedcapi.c (GH-15…
pythongh-155561: Use multi-phase init for Modules/_testlimitedcapi.c (p…
[3.15] gh-155561: Build most _testlimitedcapi files with Py_TARGET_AB…
vstinner commentedon Oct 20, 2026
Most parts of _testlimitedcapi are now built with the limited C API on Free Threading.
Modules/_testlimitedcapi.cdoesn't usePySlotAPI because WASI builds_testlimitedcapias a built-in module, and built-in module are expected to implement aPyInitfunction. Adding support for PyExport functions in Modules/config.c is quite complicated. I prefer to stop here.