New submission from Maurizio Zucchelli <mauzuc90@yahoo.it>: The documentation for contextlib.ExitStack (https://docs.python.org/3.7/library/contextlib.html#replacing-any-use-of-try...) shows an helper class (Callback) to perform cleanup using a callback. Problem is, Callback.cancel() calls ExitStack.pop_all(), which in turn calls type(self)(), this is not a valid constructor for Callback, since it always expects at least one element. (I have marked only Python 3.4 and 3.6 since those are the versions where I verified this, but it likely applies to every version.) ---------- assignee: docs@python components: Documentation messages: 307037 nosy: Denaun, docs@python priority: normal severity: normal status: open title: Wrong ExitStack Callback recipe type: crash versions: Python 3.4, Python 3.6 _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue32145> _______________________________________