Hi, The docs have this rule for slot initialization for the benefit of Cygwin: https://github.com/python/cpython/commit/db6a569de7ae595ada53b618fce6bbbd1c9... Synopsis -------- - PyType_GenericNew, /* tp_new */ + noddy_NoddyType.tp_new = PyType_GenericNew; + if (PyType_Ready(&noddy_NoddyType) < 0) + return; This is absolutely not required by C99 (and probably never was). 'PyType_GenericNew' is an address constant, and MSVC supports it just fine -- at least since VS 2008. Does anyone know if Cygwin still misbehaves? I would like to get rid of this arcane rule. https://bugs.python.org/issue31443 Stefan Krah