I'm not really worry that much over O(n^2) performace (especially having optimized some O(n^3) SQL operations :-o !)
The things is this really should be an O(n) operation. Having a yield all statement or expression is useful in its own right and also potentially a way to optimized away the O(n^2) issue. -- http://mail.python.org/mailman/listinfo/python-list
