False positive on comprehensions in class scope

[Ben Darnell]

Pyflakes reports "undefined name A" on the third line of this code:

class C(object):
    A = [1, 2, 3]
    B = dict((i, str(i)) for i in A)

This construction works in every version of Python since at least 2.5. (real-world use case from which this was extracted: https://github.com/facebook/tornado/blob/master/tornado/options.py#L444)

[asmeurer (asmeurer)]

Changing the except clause at line 444 to also catch ClassScope fixes it, i.e.,

diff --git a/pyflakes/checker.py b/pyflakes/checker.py
index ed9381e..6ed7f9c 100644
--- a/pyflakes/checker.py
+++ b/pyflakes/checker.py
@@ -441,7 +441,7 @@ class Checker(object):
         importStarred = self.scope.importStarred
         for scope in self.scopeStack[-2:0:-1]:
             importStarred = importStarred or scope.importStarred
- if not isinstance(scope, FunctionScope):
+ if not isinstance(scope, (FunctionScope, ClassScope)):
                 continue
             try:
                 scope[name].used = (self.scope, node)

But I'm not sure what the implications of this change are. It seems to lead to some test failures (which I cannot understand how to read).

[Florent (florent.x)]

Another test case from issue #1190075 (marked duplicate)

class A:
    T = range(10)

    X = {x for x in T}
    Y = {x:x for x in T}
    Z = (x for x in T)
    L = [x for x in T]

I tried the patch proposed by @asmeurer and it fixes the issue.
However it gives a failure in another part of the test suite. Under investigation...

[Florent (florent.x)]

Patch attached.