[Python-ideas] Float range class

[M.-A. Lemburg]

On 09.01.2015 12:01, Chris Angelico wrote:
> On Fri, Jan 9, 2015 at 9:55 PM, M.-A. Lemburg <mal at egenix.com> wrote:
>>> This is what I am talking about.  The idea would be to have something that
>>> is, as much as possible, identical to the existing range.  I understand it
>>> has floating-point issues, but any other approach would as well.
>>
>> This should do the trick:
>>
>> def frange(start, stop, steps):
>>     start = float(start)
>>     stop = float(stop)
>>     steps = int(steps)
>>     for i in range(steps + 1):
>>         yield ((steps - i) * start + i * stop) / steps
> 
> Thing is, a range object is a lot more than just an iterable. In many
> ways, it acts just like list(self) would - you can index it, slice it,
> etc:
> 
>>>> r = range(10, 101, 10)
>>>> list(r)
> [10, 20, 30, 40, 50, 60, 70, 80, 90, 100]
>>>> r.index(70)
> 6
>>>> r[6]
> 70
>>>> len(r)
> 10
>>>> r[1:-4:2]
> range(20, 70, 20)
> 
> Does frange() need to be able to do all these operations?

Probably 95% of all uses of range() in my own code never use range
object features beyond that of being iterable. For everything
else you can create either a list or throw itertools at it :-)

IMO, the only reason for having an frange() function in (probably)
the math module is to provide an implementation which tries to
reduce fp rounding problems to a minimum.

Other than that, it's just too simple to add straight to the
application code in a way which exactly fits the purpose and
functionality needed by that application. For decimals and
date/time values, the naive algorithm is good enough, so the
above argument doesn't apply to those.

-- 
Marc-Andre Lemburg
eGenix.com

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