[Python-Dev] Why is nb_inplace_power ternary?

[Raymond Hettinger]

[MvL]
>>>>> 1. For 2.5.1, rewrite slot_nb_inplace_power to raise an exception
>>>>> if the third argument is not None, and then invoke __ipow__ with only one 
>>>>> argument.

[Raymond]
>> Why would you change Py2.5?  There is no bug here.

[MvL]
> There is: slot_nb_inplace has the signature
>
> static PyObject * slot_nb_inplace_power(PyObject *self, PyObject * arg1)
>
> yet it is stored in as_number.nb_inplace_power, which is defined as
>
> typedef PyObject * (*ternaryfunc)(PyObject *, PyObject *, PyObject *);
> ternaryfunc nb_inplace_power;
>
> This has undefined behavior. Even if it had, slot_nb_inplace_power
> would silently discard its third argument.

That made sense, but my question was whether there would be benefit
to making the change in the middle of a major release.  At worst, code that is
currently working due to undefined behavior will stop working.   I don't
see any offsetting benefit.  ISTM that Py2.5 should be left as-is and that
the full signature change be made in Py2.6.


Raymond