[Python-Dev] PEP 576

Jeroen Demeyer J.Demeyer at UGent.be
Wed Jun 27 06:00:54 EDT 2018

On 2018-06-26 21:43, Mark Shannon wrote:
> https://github.com/markshannon/pep-576

This actually looks close to Victor Stinner's bpo-29259. But instead of 
storing the function pointer in the class, you're storing it in the 

One concern that I have is that this might lead to code duplication. You 
require that every class implements its own specialized 
_FOO_FastcallKeywords() function. So you end up with 
_PyCFunction_FastCallKeywords(), _PyMethodDescr_FastCallKeywords(), 
_PyFunction_FastCallKeywords(). If I want to implement a similar class 
myself, I have to reinvent that same wheel again. With PEP 580, I 
replace all those _FOO_FastCallKeywords() functions by one 
PyCCall_FASTCALL() function. Admittedly, my PyCCall_FASTCALL() is more 
complex than each of those _FOO_FastcallKeywords() individually. But 
overall, I think that PEP 580 leads to simpler code.

Second, you still have a performance problem for methods. You made sure 
that the method optimizations in the Python bytecode interpreter 
continue to work, but method calls from C will be slowed down. I don't 
know to what extent and whether it really matters, but it's something to 


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