Cloudpickling of class variable fails for subclass of typing.Generic

[dannyfriar]

Related to: #440

Run the following to create the object and cloudpickle to disk:

import typing
import cloudpickle

T = typing.TypeVar("T")

class Base(typing.Generic[T]):    
    foo = "bar"
    
class Child(Base):
    pass

child = Child()

with open("test.pkl", "wb") as f:
    cloudpickle.dump(child, f)

Then if load in another Python process:

import cloudpickle

with open("test.pkl", "rb") as f:
    obj = cloudpickle.load(f)
    
print(obj.foo)

Gives AttributeError: 'Child' object has no attribute 'foo'

Using cloudpickle==2.0.0 and python version 3.8.12. Observed on both Windows 10 and CentOS 8.4.

The above example works correctly (i.e. does not throw the AttributeError) with cloudpickle==2.0.0 and python version 3.6.6.

[dannyfriar]

Also fails if you modify the above to set a property on the parent class:

class Base(typing.Generic[T]):    
    @property
    def foo(self):
        return "bar"

[pierreglaser]

Hi @dannyfriar, thanks for the report. We'll fix this in #448. Also, is:

import typing
import cloudpickle

T = typing.TypeVar("T")

class Base(typing.Generic[T]):    
    foo = "bar"
    
class Child(Base):
    pass

a legitimate typing use-case? Regardless of the answer, we'll fix this issue in cloudpickle, but I'm just curious.

[dannyfriar]

Thanks @pierreglaser. I think this is a legitimate use case (obviously not the dummy example here). A better example from the mypy docs: https://mypy.readthedocs.io/en/stable/generics.html

[dannyfriar]

@pierreglaser is it possible to merge #448 now?

[pierreglaser]

Closed by #448