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Fri Feb 14 11:13:43 CET 2014 · https://mail.python.org/pipermail/python-dev/2014-February/132337.html

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).

We could theoretically do something similar, but the NULL handling in
SQL is a frequent source of bugs in filter definitions, so that really
doesn't sound like a good idea.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia

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