[Python-ideas] Implement comparison operators for range objects

[Steven D'Aprano]

Sven Marnach wrote:
> There are circumstances, for example in unit testing, when it might be
> useful to check if two range objects describe the same range.
> Currently, this can't be done using the '==' operator:
> 
>     >>> range(5) == range(5)
>     False
[...]
> All other built-in sequence types (that is bytearray, bytes, list,
> str, and tuple) define equality by "all items of the sequence are
> equal".  I think it would be both more consistent and more useful if
> range objects would pick up the same semantics.

I can see how that would be useful and straightforward, and certainly 
more useful than identity based equality. +1


> When implementing '==' and '!=' for range objects, it would be natural
> to implement the other comparison operators, too (lexicographically,
> as for all other sequence types).

I don't agree. Equality makes sense for ranges: two ranges are equal if 
they have the same start, stop and step values. But order comparisons 
don't have any sensible meaning: range objects are numeric ranges, 
integer-valued intervals, not generic lists, and it is meaningless to 
say that one range is less than or greater than another.

Which is greater?

range(1, 1000000, 1000)
range(1000, 10000)

The question makes no sense, and should be treated as an error, just as 
it is for complex numbers.

-1 on adding order comparison operators.



Aside:

I'm astonished to see that range objects have a count method! What's the 
purpose of that? Any value's count will either be 0 or 1, and a more 
appropriate test would be `value in range`:

 >>> 17 in range(2, 30, 3)  # like r.count(17) => 1
True
 >>> 18 in range(2, 30, 3)  # like r.count(18) => 0
False



-- 
Steven