[Python-Dev] PEP 590 discussion

[Mark Shannon]

Hi Jeroen,

On 15/04/2019 9:38 am, Jeroen Demeyer wrote:
> On 2019-04-14 13:30, Mark Shannon wrote:
>> PY_VECTORCALL_ARGUMENTS_OFFSET exists so that callables that make onward
>> calls with an additional argument can do so efficiently. The obvious
>> example is bound-methods, but classes are at least as important.
>> cls(*args) -> cls.new(cls, *args) -> cls.__init__(self, *args)
> 
> But tp_new and tp_init take the "cls" and "self" as separate arguments, 
> not as part of *args. So I don't see why you need 
> PY_VECTORCALL_ARGUMENTS_OFFSET for this.

Here's some (untested) code for an implementation of vectorcall for 
object subtypes implemented in Python. It uses 
PY_VECTORCALL_ARGUMENTS_OFFSET to save memory allocation when calling 
the __init__ method.

https://github.com/python/cpython/commit/9ff46e3ba0747f386f9519933910d63d5caae6ee#diff-c3cf251f16d5a03a9e7d4639f2d6f998R3820

Cheers,
Mark.