[Python-ideas] math.inf and math.nan constants

[Case Van Horsen]

On Mon, Jan 12, 2015 at 7:02 PM, Alexander Belopolsky
<alexander.belopolsky at gmail.com> wrote:
>
> On Mon, Jan 12, 2015 at 9:39 PM, Steven D'Aprano <steve at pearwood.info>
> wrote:
>>
>> As an alternative to float methods, perhaps the math module could be
>> more polymorphic, so we could write things like (say):
>>
>> math.sqrt(some_decimal)
>
>
> Something like this is trivial to implement using the singledispatch module,
> but when you are faced with the functions of two arguments such as pow,
> things get hairier.  What type should pow(2.5, Decimal(2)) return?
>
I've thought about about the following for pow(x,y), but it would
break too much existing code (i.e. when x and y are integers).

if isinstance(x, float) and isinstance(y, float):
    return the float x**y

try:
    return x.__pow__(x,y):
except TypeError:
    pass
try:
    return y.__pow__(x,y)
except TypeError:
    pass

return float(x)**float(y)

It would be nice we could distinguish "real" numbers where a real
number uses a radix, a significand, and an exponent to represent a
number. A float uses a radix of 2, a significant of 53 bits, and
limited exponent range. A Decimal uses a radix of 10, a significand of
arbitrary precision, and a (usually) wide exponent range. Both float
and Decimal would be instances of real numbers. Then the following
might work:

if isinstance(x, real) and isinstance(y, real):
    try:
        return x.__pow__(x,y):
    except TypeError:
        pass
    try:
        return y.__pow__(x,y)
    except TypeError:
        pass

return float(x)**float(y)

casevh


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