[Python-ideas] Decimal literal?

[Bruce Leban]

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.

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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