Comprehension in class scope should see class variables

[gvanrossum]

Example:

class C:
    A = 'abc'
    B = [c for c in A]

This is valid Python code, but mypy doesn't believe that A exists. (Note that it's specific to comprehensions and generator expressions -- if I put a plain C = A.lower() there it works fine.)

[JukkaL]

Marking this as priority because this also affects unannotated code (class bodies).

[gvanrossum]

That's fixed, but there's a followup issue where there's a difference between Python 2 and 3. In the following, the reference to A in the condition or in the target expression is valid in Python 2 but not in 3:

class C:
    A = 'abc'
    B = [c for c in 'abcde' if c in A]
    C = [A+c for c in 'abcde']

[gvanrossum]

(This is lower priority I haven't seen this in the wild yet.)

[JukkaL]

Clarification: In Python 2, this example works at runtime but mypy generates an error about A:

class C:
    A = 'abc'
    B = [c for c in 'abcde' if c in A]  # 'A' is not defined
    C = [A+c for c in 'abcde']  # 'A' is not defined

In Python 3 mode mypy works as expected.

[JukkaL]

Closing due to Python 2 feature freeze (#12237).