Octal notation: severe deprecation

[Bengt Richter]

On Thu, 13 Jan 2005 08:18:25 -0500, Peter Hansen <peter at engcorp.com> wrote:

>and-google at doxdesk.com wrote:
>> In Mythical Future Python I would like to be able to use any base in
>> integer literals, which would be better. Example random syntax:
>> 
>> flags= 2x00011010101001
>> umask= 8x664
>> answer= 10x42
>> addr= 16x0E800004  # 16x == 0x
>> gunk= 36x8H6Z9A0X
>
>I think I kinda like this idea.  Allowing arbitrary values,
>however, would probably be pointless, as there are very
>few bases in common enough use that a language should make
>it easy to write literals in any of them.  So I think "36x"
>is silly, and would suggest limiting this to 2, 8, 10, and
>16.  At the very least, a range of 2-16 should be used.
>(It would be cute but pointless to allow 1x000000000. :-)
>
My concern is negative numbers when you are interested in the
bits of a typical twos-complement number. (BTW, please don't tell me
that's platform-specific hardware oriented stuff: Two's complement is
a fine abstraction for interpreting a bit vector, which is another
fine abstraction ;-)

One way to do it consistently is to have a sign digit as the first
digit after the x, which is either 0 or base-1 -- e.g., +3 and -3 would be

    2x011 2x101
    8x03  8x75
    16x03 16xfd
    10x03 10x97

Then the "sign digit" can be extended indefinitely to the left without
changing the value, noting that -3 == 97-100 == 997-1000) and similarly
for other bases: -3 == binary 101-1000 == 111101-1000000 etc. IOW, you just
subtract base**<number of digits in representation> if the first digit
is base-1, to get the negative value.

This would let us have a %<width>.<base>b format to generate the digits part
and would get around the ugly hack for writing hex literals of negative numbers.

    def __repr__(self): return '<%s object at %08.16b>' %(type(self).__name__, id(self))

and you could write based literals in the above formats with e.g., with
    '16x%.16b' % number
or
    '2x%.2b' % number
etc.

Regards,
Bengt Richter