[Python-Dev] Deprecation warning on integer shifts and such

[Martin v. Loewis]

Oren Tirosh <oren-py-d@hishome.net> writes:

> >>> hex(-16711681)
> '0xff00ffff'
> >>> hex(-16711681L)
> '-0xff0001L'		# ??!?!?
[...] 
> The hex representation of longs is something I find quite misleading and 
> I think it's also unprecedented.  This wart has bothered me for a long 
> time now but I didn't have any use for it so I didn't mind too much. Now 
> it is proposed to extend this useless representation to ints so I do.

I don't find it misleading - in fact, the C representation is
misleading: 0xff00ffff looks like a positive number (it does not have
a sign) - this is misleading, as the number is, in fact, negative.

The representation is not misleading: it does not make you believe it
is something that it actually isn't. It might be surprising, but after
thinking about it, it should be clear that it is correct: -N is the
number that, when added to N, gives zero. Indeed:

>>> -16711681L+0xff0001L
0L

If you want the bitmask for the lowest 32 bits, you can write

>>> hex(-16711681L & (2**32-1))
'0xFF00FFFFL'

Notice that -16711681 is a number with an infinite amont of leading
ones - just as 16711681 is a number with an infinite amount of leading
zeroes.

Regards,
Martin