Xiang Zhang added the comment: +1 for jsoh. Actually the behaviour is documented in https://docs.python.org/3/reference/expressions.html#value-comparisons. So a single 'a is b' or 'a == b' is not complete. I would like to use 'equal to' which implies 'a is b or a == b'. ---------- nosy: +xiang.zhang _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue29756> _______________________________________