[Python-Dev] Why is nb_inplace_power ternary?

["Martin v. Löwis"]

Brett Cannon schrieb:
> Seems reasonable to me.  Is the argument of None passed in
> automatically somewhere?  

There are few callers of nb_inplace_power at all (AFAICT, only
PyNumber_InPlacePower); in turn, PyNumber_InPlacePower is called
with the implicit Py_None always:
- ceval.c, for INPLACE_POWER (which is binary)
- operator.ipow (which is also binary)
- class.c, from bin_inplace_power, which in turn is called from
   instance_ipow if the instance's 3rd argument to
   nb_inplace_power is Py_None (if there is a non-None third
   argument, instance_ipow invokes __ipow__ with three arguments
   if __ipow__ is defined, else it invokes __pow__ with three
   arguments)

The only case I could find where a third argument is non-None
is when the builtin pow() is invoked, which then invokes nb_power
(but not nb_inplace_power) with three arguments.

Regards,
Martin