On Thu, 13 Jan 2005 08:18:25 -0500, Peter Hansen <(E-Mail Removed)> wrote:

>(E-Mail Removed) 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