Attached PR 14142 fix bpo-34646 regression. > It shouldn't break existing code because PyRun_String has a macro expansion to PyRun_StringFlags. ABI compatibility between major releases is not provided. Many applications don't use Python header files, but access directly libpython. For example, py2app uses dlsym(): https://bitbucket.org/ronaldoussoren/py2app/src/default/py2app/apptemplate/src/main.c PyInstaller uses GetProcAddress() on Windows or dlsym() on other platforms: * https://github.com/pyinstaller/pyinstaller/blob/1844d69f5aa1d64d3feca912ed1698664a3faf3e/bootloader/src/pyi_python.h * https://github.com/pyinstaller/pyinstaller/blob/1844d69f5aa1d64d3feca912ed1698664a3faf3e/bootloader/src/pyi_pythonlib.c That's why PyRun_String() is defined as an alias using a macro *and* as a function in pythonrun.c: #undef PyRun_String PyObject * PyRun_String(const char *str, int s, PyObject *g, PyObject *l) { return PyRun_StringFlags(str, s, g, l, NULL); }