[Python-ideas] Float range class

[Joao S. O. Bueno]

Since this is being carried on, I see that many of the problems
resulting from a naive use of FP would not happen with
Decimals  -
Why not either allow the frange to have it's type specified
(among float/Decimal/fraction/etc...) or, to keep things simple and boring,
just  think about one *range function for Decimals as well?



On 9 January 2015 at 08:55, M.-A. Lemburg <mal at egenix.com> wrote:
> On 08.01.2015 18:12, Todd wrote:
>> On Thu, Jan 8, 2015 at 5:18 PM, M.-A. Lemburg <mal at egenix.com> wrote:
>>> I think you'd first have to describe some use cases, since it's
>>> not at all clear what you mean with "float range", e.g. you
>>> could be referring to:
>>>
>>> * interval arithmetics: http://en.wikipedia.org/wiki/Interval_arithmetic
>>>
>>> * ranges of numbers with a fixed stepping (which can create problems
>>>   near the edges due to rounding issues)
>>>
>>
>> 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
>
> It's a generator. If you need a list, wrap it into list(frange(...)).
>
> The calculation may look a little awkward. That's on purpose to
> reduce fp rounding errors.
>
> tmp/frange> python3.4 -i frange.py
>>>> list(frange(0,1,3))
> [0.0, 0.3333333333333333, 0.6666666666666666, 1.0]
>>>> list(frange(0,1,4))
> [0.0, 0.25, 0.5, 0.75, 1.0]
>>>> list(frange(0,1,5))
> [0.0, 0.2, 0.4, 0.6, 0.8, 1.0]
>>>> list(frange(0,1,6))
> [0.0, 0.16666666666666666, 0.3333333333333333, 0.5, 0.6666666666666666, 0.8333333333333334, 1.0]
>>>>
>
> Both sides of the range are included. If you need one side open, simply
> leave out the first or last element of the list.
>
> --
> Marc-Andre Lemburg
> eGenix.com
>
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