[Python-ideas] Add the imath module

[Steven D'Aprano]

On Fri, Jul 13, 2018 at 10:56:21AM +1000, Chris Angelico wrote:

> You can say that about algorithms easily enough. My point is that this
> ought to be a constraint on the function - implementations may choose
> other algorithms, but they MUST follow one pattern or the other,
> meaning that a Python script can depend on it without knowing the
> implementation. Like guaranteeing that list.sort() is stable without
> stipulating the actual sort algo used.

I cannot imagine an algorithm that wasn't totally brain-dead (like "flip 
a coin") which could wrongly report a prime number as composite. Maybe 
I'm not imaginative enough :-)

But yeah, if you want to formally specify that any such isprime test 
will never have false negatives (never report an actual prime as 
composite), sure thing. I think that's stating the bleeding obvious, 
like demanding that any algorithm we use for factorial(n) must not 
return the sqrt of n by mistake, but whatever :-)

I suppose that if you cared more about running time than correctness, 
one might simply report anything bigger than (let's say) 2**20 as 
"composite". But I call that "brain dead" :-)



-- 
Steve