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Tue Jun 21 12:16:17 CEST 2005 · http://mail.python.org/pipermail/python-dev/2005-June/054391.html

On 6/20/05, Keith Dart <kdart at kdart.com> wrote:
> On Mon, 20 Jun 2005, Guido van Rossum wrote:
[...]
> > By far the easiest way to do arithmetic mod 2**32 is to just add "&
> > 0xFFFFFFFF" to the end of your expression. For example, simulating the
> > effect of multiplying an unsigned long by 3 would be x = (x * 3) &
> > 0xFFFFFFFF.
> 
> But then I wouldn't know if it overflowed 32 bits.

Huh? C unsigned ints don't flag overflow either -- they perform
perfect arithmetic mod 2**32.

> In my usage, the
> integer will be translated to an unsigned (32 bit) integer in another
> system (SNMP). I want to know if it will fit, and I want to know early if
> there will be a problem, rather than later (at conversion time).

So check if it is >= 2**32 (or < 0, of course).

> One of the "selling points" of Python in previous versions was that you
> would get an OverFlowError on overflow, where other languages did not
> (they overflowed silently). So I subclassed long in 2.3, to get the same
> overflow exception:
>          ...
> Again, because I want to catch the error early, before conversion to the
> external type.

This is a very specialized application. Your best approach is to check
for overflow before passing into the external API -- ideally the
wrappers for that API should do so.

> > If there is a problem with ioctl() not taking long ints, that would be
> > a bug in ioctl, not a lacking data type or a problem with long ints.
> 
> That must be it, then. Shall I file a bug somewhere?

SourceForge. (python.org/dev for more info)

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)

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[Python-Dev] Is PEP 237 final -- Unifying Long Integers and Integers