[Python-ideas] Negative hexes

[Guido van Rossum]

On Sat, Dec 3, 2011 at 5:32 PM, MRAB <python at mrabarnett.plus.com> wrote:

> On 04/12/2011 01:17, Guido van Rossum wrote:
>
>> On Sat, Dec 3, 2011 at 5:13 PM, Nick Coghlan <ncoghlan at gmail.com
>> <mailto:ncoghlan at gmail.com>> wrote:
>>
>>    On Sun, Dec 4, 2011 at 3:07 AM, Antoine Pitrou <solipsis at pitrou.net
>>    <mailto:solipsis at pitrou.net>> wrote:
>>     >> This is because Python's integers are not limited to 32 bits or
>>    64 bits. If
>>     >> you read PEP 237, you'll see that this was one of the hardest
>>    differences
>>     >> between ints and longs to be resolved. You'd have to include an
>>    infinite
>>     >> number of leading 'F' characters to format a negative long this
>>    way...
>>     >
>>     > That's a fair point :)
>>
>>    Random thought... could we use the integer precision field to fix
>>    *that*, by having it indicate the intended number of bytes in the
>>    integer?
>>
>>    That is, currently:
>>
>>     >>> "{:.4x}".format(31)
>>    Traceback (most recent call last):
>>      File "<stdin>", line 1, in <module>
>>    ValueError: Precision not allowed in integer format specifier
>>
>>    What if instead that produced:
>>
>>     >>> "{:.4X}".format(31)
>>    0000001F
>>     >>> "{:.4X}".format(-31)
>>    FFFFFFE1
>>
>> Usually that field is measured in characters/digits, so this should
>> probably produce FFE1; you'd need {:.8X} to produce FFFFFFE1. This would
>> then logically extend to binary and octal, in each case measuring
>> characters/digits in the indicated base.
>>
>>  +1
>
> Not only would that be more consistent, it would also have a use-case.


OTOH I'm not sure what should happen if the number (negative or positive!)
doesn't fit in the precision.

How common is this use case? Personally I'm fine with writing x & (2**N -
1) where N is e.g. 32 or 64.

-- 
--Guido van Rossum (python.org/~guido)
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