[Python-Dev] python 3 niggle: None < 1 raises TypeError

[Antoine Pitrou]

On Fri, 14 Feb 2014 20:13:43 +1000
Nick Coghlan <ncoghlan at gmail.com> wrote:
> On 14 February 2014 20:02, Antoine Pitrou <solipsis at pitrou.net> wrote:
> > On Fri, 14 Feb 2014 10:46:50 +0100
> > Lennart Regebro <regebro at gmail.com> wrote:
> >> >
> >> > Sending this to python-dev as I'm wondering if this was considered when the
> >> > choice to have objects of different types raise a TypeError when ordered...
> >> >
> >> > So, the concrete I case I have is implementing stable ordering for the
> >> > python Range objects that psycopg2 uses. These have 3 attributes that can
> >> > either be None or, for sake of argument, a numeric value.
> >> >
> > [...]
> >>
> >> It was considered. It's not obvious where you want "None" to appear in
> >> your ordering, so you will have to implement this by yourself. I can't
> >> come up with anything obviously shorter.
> >
> > I have to agree with Lennart. The fact that SQL defines an order for
> > NULL and other values doesn't mean it's obvious or right in any way (I
> > never remember which way it goes).
> 
> SQL doesn't define an order for NULL, it's more like a "quiet NaN" -
> if either operand is NULL, the result is also NULL. (I ran into this
> recently, in the context of "NULL == value" and "NULL != value" both
> being effectively false).

Hmm, it seems you're right, but I'm quite sure some DBMSes have a
consistent way of ordering NULLs when using ORDER BY on a nullable
column.

Regards

Antoine.