[Python-Dev] PEP 590 vs. bpo-29259 (original) (raw)

Jeroen Demeyer J.Demeyer at UGent.be
Wed Apr 3 11:41:06 EDT 2019

As I'm reading the PEP 590 reference implementation, it strikes me how similar it is to https://bugs.python.org/issue29259

The main difference is that bpo-29259 has a per-class pointer tp_fastcall instead of a per-object pointer. But actually, the PEP 590 reference implementation does not make much use of the per-object pointer: for all classes except "type", the vectorcall wrapper is the same for all objects of a given type.

One thing that bpo-29259 did not realize is that existing optimizations could be dropped in favor of using tp_fastcall. For example, bpo-29259 has code like

 if (PyFunction_Check(callable)) {
     return _PyFunction_FastCallKeywords(...);
 }
 if (PyCFunction_Check(callable)) {
     return _PyCFunction_FastCallKeywords(...);
 }
 else if (PyType_HasFeature(..., Py_TPFLAGS_HAVE_FASTCALL) ...)

but the first 2 branches are superfluous given the third.

Anyway, this is just putting PEP 590 a bit in perspective. It doesn't say anything about the merits of PEP 590.

Jeroen.

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