Note that genexps are function scopes too and therefore won't see class attributes.
diff --git a/Doc/reference/executionmodel.rst b/Doc/reference/executionmodel.rst
index 69a6259..c5a24e9 100644
--- a/Doc/reference/executionmodel.rst
+++ b/Doc/reference/executionmodel.rst
@@ -52,7 +52,13 @@
definition occurs in a function block, the scope extends to any blocks contained
within the defining one, unless a contained block introduces a different binding
for the name. The scope of names defined in a class block is limited to the
-class block; it does not extend to the code blocks of methods.
+class block; it does not extend to the code blocks of methods -- this includes
+generator expressions since they are implemented using a function scope. This
+means that the following will fail::
+
+ class A:
+ a = 42
+ b = list(a + i for i in range(10))
.. index:: single: environment