In this example (from #982) we define an attribute via assignment in __new__:

class C(object):
    def __new__(cls, foo=None):
        obj = object.__new__(cls)
        obj.foo = foo
        return obj

x = C(foo=12)
print(x.foo)

Currently mypy doesn't recognize attribute foo and complains about x.foo. To implement this, we could do these things:

• Infer the fact that obj is something similar to self because of the way is created via object.__new__. This should happen during semantic analysis so that this will work in unannotated method as well.
• Infer attributes from assignments via obj because it is classified as similar to self.
• Also recognize object.__new__ calls via super(...).