STINNER Victor <report@bugs.python.org> wrote:
> decimal.Decimal.__truediv__() has an optional context argument, whereas _decimal defines PyNumberMethods.

Regarding the special methods: decimal.py uses the optional context arguments
for convenience so that these methods can be re-used in other places.

I wouldn't consider this context argument as part of the API.

> decimal.Decimal.quantize() second argument is optional and its default value
> is None, but if I pass None to _decimal.Decimal.quantize(), I get a TypeError
> because _decimal expects an integer.

About this I'm not sure. I think type errors are a courtesy to the user.
Look what is possible now in decimal.py:

Decimal('9')

But here the argument might well be made for accepting None (and only
None apart from rounding modes). - I hope Mark and Raymond will give
their opinions, too.