[Python-ideas] Changing Decimal.__pos__ and Decimal.__neg__ [Was: Re: Python Numbers as Human Concept Decimal System]

[Tim Peters]

[Mark Dickinson <dickinsm at gmail.com>]
>> >>> -Decimal(0.0)  # negative sign mysteriously disappears.
>>
>> Decimal('0')

[Stefan Krah <stefan at bytereef.org>]
> Unless the rounding mode is ROUND_FLOOR. :(
>
> >>> getcontext().rounding = ROUND_FLOOR
> >>> -Decimal(0.0)
> Decimal('-0')

I may be missing something, but our docs don't appear to be clear
about what unary minus means in Python's decimal implementation.

Looks like Mike C's intent was that

    +x

act like

    Decimal(0) + x

and

    -x

like

    Decimal(0) - x

Then all the examples "make sense" (given that you think the
standards' rules for adding/subtracting signed zeros make sense).

Can't win!  That -x loses the sign when x is a positive 0 (under most
rounding modes) is jarring; but that the results of "-x" and "0-x" may
not be the same would also be jarring.

Not a fan of signed zeroes :-(