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[Python-Dev] Stable ABI or not for PyTypeObject?


Hello,

I have a simple question for which there doesn't seem to be a good 
answer: is the layout of PyTypeObject considered to be part of the 
stable ABI?

Officially, the answer is certainly "no" (see PEP 384).

However, unofficially the answer might be "yes". At least, the last time 
that an incompatible change was made to PyTypeObject (adding tp_finalize 
in Python 3.4, PEP 442), care was taken not to break the ABI by using 
the Py_TPFLAGS_HAVE_FINALIZE flag.

There is some discussion about this on https://bugs.python.org/issue32388

The implementation of PEP 590 is going to make another ABI-breaking 
change. So should we add a new Py_TFLAGS_HAVE_... flag for that or not?


Jeroen.