One of my coworkers just stumbled across an interesting issue. I'm hoping someone here can explain why it's happening.
When trying to create a class with a dual-loop generator expression in a class definition, there is a strange scoping issue where the inner variable is not found, (but the outer loop variable is found), while a list comprehension has no problem finding both variables. Demonstration: >>> class Spam: ... foo, bar = 4, 4 ... baz = dict(((x, y), x+y) for x in range(foo) for y in range(bar)) ... Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 3, in Spam File "<stdin>", line 3, in <genexpr> NameError: global name 'bar' is not defined >>> class Eggs(object): ... foo, bar = 4, 4 ... baz = dict([((x, y), x+y) for x in range(foo) for y in range(bar)]) ... >>> This was discovered in python 2.6. In python 3.2, both versions fail with the same NameError. Obviously, this is easy enough to work around. I'm curious though: What's going on under the hood to cause the nested generator expression to fail while the list comprehension succeeds? Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
