[Python-Dev] Re: Decimal type question [Prothon]

[Andrew P. Lentvorski, Jr.]

On Aug 9, 2004, at 10:29 AM, Mark Hahn wrote:

> Forgive me if I'm being a pest, but no one has commented on the real 
> reason
> I asked the question.  What does everyone think of the idea of having 
> these
> three built-in numeric types?
>
> 1) An Int implemented with infinite precision integer (Python Longs) 
> with
> the constant/__str__ form of +-NN such as 0, -123, 173_394, etc.
>
> 2) A Decimal implemented with the .Net decimal float (or the IBM 
> decimal if
> the .Net decimal sucks too much) with the constant/__str__ form of 
> +-NN.NN
> such as 0.0, -123.0, 173_394.0, 173394.912786765, etc.
>
> 3) A binary Float implemented with the hardware floating point with the
> constant/__str__ form of +-NN.NN+-eNN such as 0e0, -123e0, 173.39e+3,
> 2.35e-78, etc.

Be careful defining string representations of numbers.  It is a 
non-trivial
problem to adhere to the correct internationalization standards.

Forgive me if I'm being dense, but don't we already have 1 & 3 as built
in types?

2 is unlikely to be a builtin until folks get some experience using the
Decimal module.  Yes, the .Net Decimal sucks.

In addition, the desired evolution of Python seems to be replacing the
binary floating point as the default floating point type with the
decimal floating point type by default rather than growing another
builtin numeric type.  This is obviously contingent upon the Decimal 
module
getting some real-life use as well as it getting some speed improvements
in the future.

> There would be no automatic conversion except the / operator would 
> convert
> from Int to Decimal

Int goes to the default type of float (which is currently binary FP) 
already
upon using the / operator.

>  and the Math module would convert Int and Decimal
> values to Float for almost all functions (except simple ones like abs, 
> min,
> max).

This is not necessarily a good idea.  Exponentials are very useful in
financial situations and want to be decimals, not binary floats, in 
those
cases.

-a