[Python-ideas] Decimal literal?

[Chris Rebert]

On Fri, Dec 5, 2008 at 2:02 PM, Bruce Leban <bruce at leapyear.org> wrote:
> There is a representation for decimal literals that nicely avoids the
> problem of remembering that 0d is decimal and 0m is meters etc.:
>
>>>> import decimal
>>>> decimal.Decimal(3)
> Decimal("3")
>>>> Decimal("3")
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
> NameError: name 'Decimal' is not defined
>
> The error points out that I really need to do both:
>
>>>> import decimal
>>>> from decimal import Decimal.

You only need the second line there. The first line is unnecessary and
does not effect the second.

Cheers,
Chris

-- 
Follow the path of the Iguana...
http://rebertia.com

>
> and I'd prefer the single import do both. Note that this anomaly of repr is
> not limited to decimal as I think this is a bit worse:
>
>>>> float('nan')
> nan
>>>> float('inf')
> inf
>
> --- Bruce
>
> On Fri, Dec 5, 2008 at 10:53 AM, Jim Jewett <jimjjewett at gmail.com> wrote:
>>
>> On Thu, Dec 4, 2008 at 4:45 AM, Cesare Di Mauro
>> <cesare.dimauro at a-tono.com> wrote:
>> > But at least it will be more usable to have a
>> > short-hand for decimal declaration:
>>
>> In isolation, a decimal literal sounds nice.
>>
>> But it may not be used often enough to justify the extra mental
>> complexity.
>>
>> What should the following mean?
>>
>> >>> a = 123X
>>
>> It isn't obvious, which means that either it gets used all the time
>> (decimal won't) or people will have to look it up -- or just guess,
>> and sometimes get it wrong.
>>
>> > a = 1234.567d
>>
>> To someone who hasn't programmed much with decimal floating point,
>> what does the "d" mean?
>>
>> Could it indicate "use double-precision"?
>>
>> Could it just mean that the written representation is "decimal" as
>> opposed to "octal" or "hexadecimal", but that the internal form is
>> still binary?
>>
>> > a = 1234.567d
>>
>> > is simpler than:
>>
>> [reworded to be even shorter per use]
>>
>> >>> from decimal import Decimal as d
>> >>> a = d('1234.5678')
>>
>> but if you really have enough Decimal literals for the difference to
>> matter, you could always write your own helper function.
>>
>> >>> # pretend to be using the European decimal point
>> >>> a = d(1234,5678)
>>
>> >>> # maps easily to the tuple-format constructor
>> >>> a = d(12345678, -4)
>>
>> My own hunch is that until Decimal is used enough that people start
>> putting this sort of constructor into their personal libraries, it
>> probably doesn't need a literal.
>>
>> -jJ
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