Support adding class variables to class through assignment

[PeterJCLaw]

Mypy supports adding items to self during test setUp, which is great. However in many cases it's useful to be able to add items to the class during setUpClass (or Django's setUpTestData).

import unittest

class Tests(unittest.TestCase):
    @classmethod
    def setUpClass(cls) -> None:
        cls.foo = 42  # "Type[Tests]" has no attribute "foo"

    def test_foo(self) -> None:
        print(self.foo)  # "Tests" has no attribute "foo"

Adding a ClassVar allows for a workaround to this, however it would be nice if that wasn't needed.

[msullivan]

Yeah, adding to a class through a class variable write could be handy, though I doubt it is really on the roadmap for us to implement. There ought to be an issue open for it but I couldn't find one, so I'll leave this open.

[PeterJCLaw]

Ah, I'd assumed that the support for setUp was specific to unittest handling. Is it just general handling around adding properties to instances? (I had thought that mypy would normally error if you tried to add properties to instances)

[rbharadwaj9]

@PeterJCLaw can you elaborate on your workaround to this problem? I tried typing my variables in setUpClass with ClassVar but it doesn't seem to help. I think I'm going it wrong.

[PeterJCLaw]

I think I worked around this by adding the variables to the class and marking them as ClassVar there.
For example see the variable srcomp_instance in the following: https://github.com/PeterJCLaw/srcomp/blob/d3839d4578728f17a052ce934e8f6fe05a38dfad/tests/test_comp.py#L13-L19

[rbharadwaj9]

That worked for me. Thanks!