Multiplying sequences with floats

Christoph Zwerschke cito at
Fri Mar 24 22:06:30 CET 2006

Andrew Koenig wrote:
> Christoph Zwerschke wrote:
>> Anyway this would be an argument only against the variant of typecasting a 
>> float with a fractional part. But what about the other variant which 
>> raises an error if there is a fractional part, but works if the float is 
>> actually an exact integer, like the result of 4.0//2.
> I think that's a really bad idea, because of the possibility that the result 
> might happen to be an exact integer on one implementation but not another. 
> In such situations, the fact that it might fail on implementation X may well 
> be impossible to detect by any amount of testing on implementation Y.  Such 
> untestable errors are such a nuisance that it would better for the language 
> to encourage programmers to give them a wide berth.

1./20*40 == 2 or math.sqrt(4.0) == 2 may not always be True (on my 
platform it is True), but on every platform 4.0//2 == 2 should be True. 
More general, the result of a//b should always be an exact integer, and 
a//b == int(a/b) for all positive numbers a,b, no matter on which 
platform. If not, I would consider a//b broken on that platform.

And if a//b == int(a/b) is True, I think it is also reasonable to expect 
that  a//b * list  is the same as  int(a/b) * list

-- Christoph

More information about the Python-list mailing list