int/long unification hides bugs

Andrew Dalke adalke at mindspring.com
Sun Oct 31 03:34:42 CET 2004


Jeremy Fincher wrote:
> How long with this take to run?
> 
> 
>>>>a = RangedNumber(2**31, 0, 2**32)
>>>>a ** a

It wouldn't -- I didn't implement __pow__. ;)

> I think our inability to write a RangedNumber that piggybacks on
> Python's integers should be obvious.

It sounds like you don't like that the simple
__pow__ implementation will raise a MemoryError after
a long time when you would rather have it raise a
bounds violation error early.

If you want that, you could have an implementation that
uses a few logs to check for that possibility.

Though I'm not sure how to do the bounds checking for
the 3 arg form.  Given a as above, I know that

   pow(a, a, 2**50)

but without doing the computation my bounds checker
can't (or at least shouldn't) be that clever.  Should
it require that the 3rd arg always be in the allowed
range?

What about

a = RangedNumber(100, 100, 400)
pow(a, 25424134, 321)

?  It turns out the result is 321 which is in the right
range, but I can't know that without basically doing
the calculation.


				Andrew
				dalke at dalkescientific.com



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