[Python-3000] None in Comparisons: None vs. float("inf")

[Bruce Leban]

I think the behavior of NaN in comparisons is more confusing:
>>> sorted([1,nan,2])
[1, nan, 2]
>>> sorted([2,nan,1])
[2, nan, 1]
>>> sorted([2,None,1])
Traceback (most recent call last):
  File "<pyshell#28>", line 1, in <module>
    sorted([2,None,1])
TypeError: unorderable types: NoneType() < int()

At least the third case is clear that I shouldn't have done that. The way
nan works, the results of sorting where one of the values is nan is
unpredictable and useless.

Yes, I know the rules about how NaN values behave in comparisons.
Notwithstanding that, sorting could use a different comparison rule imposing
a total ordering: -inf, ..., inf, nan as some other systems do.

--- Bruce


On Thu, Nov 13, 2008 at 10:55 AM, Tim Peters <tim.peters at gmail.com> wrote:

> [M.-A. Lemburg]
> > ...
> > So far, I haven't heard a single argument for why not having None
> > participate in an ordering scheme is a good strategy to use, except
> > that it's pure.
>
> I've tracked down plenty of program logic errors that would have been
> discovered more easily if comparing None to (mostly, but among others)
> integers and strings had raised an exception instead of returning a
> meaningless true/false result.  Perhaps you haven't.  For those who
> have, the attraction to making comparisons with None refuse to return
> nonsense silently is both obvious and visceral.
>
>
> > IMHO, practicality beats purity in this special case.
>
> If hiding program logic errors is practical, sure ;-)
>
> there-is-no-behavior-no-matter-how-bizarre-someone-won't
> come-to-rely-on-ly y'rs  - tim
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