Fix enum truthiness for StrEnum #18379
Conversation
hauntsaninja
force-pushed
the
fix-enum
branch
from
f20c12f to
aab9bc3
Compare
hauntsaninja
force-pushed
the
fix-enum
branch
from
aab9bc3 to
83cf4c2
Compare
| elif isinstance(t, Instance): | ||
| if t.type.is_final or t.type.is_enum: | ||
| return UninhabitedType(line=t.line) | ||
| elif isinstance(t, LiteralType) and t.is_enum_literal(): | ||
| return UninhabitedType(line=t.line) |
There was a problem hiding this comment.
metaclasses are a red herring, enums are just effectively final, so this is safe to do
There was a problem hiding this comment.
Are you sure it's not about the order of operations? I.e. first __bool__ gets checked, then __len__ and then the same thing happens for the metaclass.
But here __bool__ gets checked and then immediately it goes to the metaclass.
I think falling back to the metaclass is correct, it just happens too early.
There was a problem hiding this comment.
Alright I had a read of the blog post, maybe metaclasses aren't involved in truthiness after all and it just so happens that the default is to return True if you have neither a __bool__ or __len__, although I'm a little confused about the purpose of __bool__ on EnumMeta, when that is the default truthiness anyways.
There was a problem hiding this comment.
I double checked, looks like the metaclass does matter, but only for the truthiness of type[Enum], not the instances.
>>> from enum import EnumMeta
>>> EnumMeta.__bool__ = lambda self: False
>>> from enum import Enum
>>> bool(Enum)
False
>>> class Foo(Enum):
... a = "a"
...
>>> bool(Foo.a)
True
>>> There was a problem hiding this comment.
That's right. It would also affect bool(Foo)
... continuing from your monkey patch ...
>>> bool(Foo)
False
>>> type(Foo.a).__mro__
(<enum 'Foo'>, <enum 'Enum'>, <class 'object'>)
>>> type(Foo).__mro__
(<class 'enum.EnumType'>, <class 'type'>, <class 'object'>)
|
According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅ |
Fixes #18376
See also https://snarky.ca/unravelling-not-in-python/