Class variable gets the type of instance variable

[roganov]

According to PEP 526, type annotations inside class bodies apply to instances unless wrapped with ClassVar. Am I misreading something or is this a bug?

class Test:
    a: int

reveal_type(Test.a + 1)

Revealed type is 'builtins.int'

[ilevkivskyi]

According to PEP 526, type annotations inside class bodies apply to instances unless wrapped with ClassVar. Am I misreading something or is this a bug?

So where is the contradiction here? The PEP doesn't say instance variables can't be set on the class. This is a relatively common pattern -- instance variable with a default (also mentioned in the PEP IIRC). The opposite however is unsafe, and therefor prohibited:

class Test:
    a: ClassVar[int]

Test().a = 1  # Error!

[PeterJCLaw]

@ilevkivskyi I think that @roganov's point is the reverse -- not that the member shouldn't be inherited by the instance, rather that the member should only be present on the instance.

[roganov]

Ideally there should be a way to specify different types for class members and instance members. I tried to implement this using descriptors, but didn't succeed.

[KotlinIsland]

The pep is slightly vague about this:

Type annotations can also be used to annotate class and instance variables in class bodies and methods. In particular, the value-less notation a: int allows one to annotate instance variables that should be initialized in __init__ or __new__.
- pep 526

While this does indicate that it shouldn't be available on the class, it doesn't explicitly rule it out.

The case from #11832 is very cut and dry though. Where the instance variables are declared within the __init__ body.

class Foo:
    def __init__(self) -> None:
        self.bar: str
        self.foo = 1
        
Foo.foo # no error
Foo.bar # no error