Comment 15 for bug 1573577

4:36 -queuebot:#ubuntu-release- Unapproved: python-qrencode (xenial-proposed/universe) [1.01-5 => 1.01-5ubuntu1~xenial] (no packageset)
14:43 <rbasak> ^ ~xenial is dangerous
14:44 <rbasak> Because xenial > artful.

In this particular case it may be fine. But please don't start that pattern, and use something like ~16.04 at least.