[issue35712] Make NotImplemented unusable in boolean context
Serhiy Storchaka
report at bugs.python.org
Wed Mar 11 17:41:19 EDT 2020
Serhiy Storchaka <storchaka+cpython at gmail.com> added the comment:
> How is -1 interpreted? Does it become a TypeError?
It is interpreted as error. It requires an exception be set. If you return -1 without setting an exception you will usually get a SystemError or crash. Oh, and this may happen during executing other code, so you will search a bug in wrong place.
You cannot change this without breaking the C and Python API in hard way.
> So my thinking is that when the interpreter gets the `NotImplemented` returned by either `if a` or by `if not a` that it would be converted to a `TypeError`
> and the `and` machinery sees it has a `NotImplemented` and raises a `TypeError`.
So you literally want NotImplemented raising a TypeError in boolean context except the "not" operator, and redefine `not a` from
False if a else True
to
NotImplemented if a is NotImplemented else False if a else True
You can do this, but this is a different issue, and I doubt that it will solve many problems.
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