[issue43908] array.array should remain immutable: add Py_TPFLAGS_IMMUTABLETYPE flag

[Erlend E. Aasland]

Erlend E. Aasland <erlend.aasland at innova.no> added the comment:

In inherit_slots() in Objects/typeobject.c, Py_TPFLAGS_HAVE_VECTORCALL inheritance depends on if the base type is a heap type or not. This aligns with PEP 590[1]:

  Heap types never inherit the vectorcall protocol because that
  would not be safe (heap types can be changed dynamically).

AFAICS, inherit_slots() should now use Py_TPFLAGS_IMMUTABLETYPE to decide if Py_TPFLAGS_HAVE_VECTORCALL can be inherited, and the PEP should be updated.


- [1] https://www.python.org/dev/peps/pep-0590/#subclassing

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