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True, except GeneratorExit will run at garbage collection time and this will result in reference cycle problems. Checking if there is no except GeneratorExit clause might be too complicated.
I still think this is worth a brief note in the gc docs. The gc docs talk only about __del__ methods, and there isn't one defined for the example generator. The generator does have something technically equivalent, but I don't spot any actual __del__ methods in the reference loop.
A docs mention will not help much in avoiding this problem, but it will at least make the code behaviour equivalent to documentation. A mention in the gc docs would have helped me when trying to debug the leak in Django.