Nick Coghlan <ncoghlan@gmail.com> added the comment: After further discussion on python-dev, it is clear that this identity checking behaviour handles more than just NaNs - it also allows containers to cope more gracefully with objects like NumPy arrays that make use of rich comparisons to return something other than simple True/False values for equality checks. Also, since I neglected to mention it in the initial post, merely *adding* the glossary entry is just the first step. It then needs to be referenced from the appropriate points in the language and library reference. ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue11945> _______________________________________