[Python-ideas] Implement comparison operators for range objects

[Nick Coghlan]

On Thu, Oct 13, 2011 at 1:18 PM, Guido van Rossum <guido at python.org> wrote:
> FWIW, I don't think the argument from numeric comparisons carries
> directly. The reason numeric comparisons (across int, float and
> Decimal) ignore certain "state" of the value (like precision or type)
> is that that's how we want our numbers to work.
>
> The open question so far is: How do we want our ranges to work? My
> intuition is weak, but says: range(0) != range(1, 1) != range(1, 1, 2)
> and range(0, 10, 2) != range(0, 11, 2); all because the arguments
> (after filling in the defaults) are different, and those arguments can
> come out using the start, stop, step attributes (once we implement
> them :-).

Between this and Raymond's point about slicing permitting easy and
cheap normalisation of endpoints, I'm convinced that, if we add direct
comparison of ranges at all, then start/stop/step comparison is the
way to go.

> PS. An (unrelated) oddity with range and Decimal:
>
>>>> range(Decimal(10))
> Traceback (most recent call last):
>  File "<stdin>", line 1, in <module>
> TypeError: 'Decimal' object cannot be interpreted as an integer
>>>> range(int(Decimal(10)))
> range(0, 10)
>>>>
>
> So int() knows something that range() doesn't. :-)

Yeah, range() wants to keep floats far away, so it only checks
__index__, not __int__. So Decimal gets handled the same way float
does (i.e. not allowed directly, but permitted after explicit coercion
to an integer).

Cheers,
Nick.

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