[Python-Dev] PEP 580 and PEP 590 comparison.

[Jeroen Demeyer]

On 2019-04-27 11:26, Mark Shannon wrote:
> Specifically, and this is important, PEP 580 cannot implement efficient
> calls to class objects without breaking the ABI.

First of all, the layout of PyTypeObject isn't actually part of the 
stable ABI (see PEP 384). So, we wouldn't be breaking anything by 
extending PyTypeObject.

Second, even if you don't buy this argument and you really think that we 
should guarantee ABI-compatibility, we can still solve that in PEP 580 
by special-casing instances of "type". Sure, that's an annoyance but 
it's not a fundamental obstruction.

Jeroen.