[Python-Dev] PEP 572: Assignment Expressions

[Tim Peters]

[Sven R. Kunze <srkunze at mail.de>]
> What about
>
> diff = x - x_base
> if diff and gcd(diff, n) > 1:
>     return gcd(diff, n)
>
> # or
>
> if (x - x_base) and gcd(x - x_base, n) > 1:
>     return gcd(x - x_base, n)
>
>
> and have the interpreter handle the optimization, or apply an lru_cache? ;-)

Surely you're joking.  This is math.gcd(), which is expensive for
multi-thousand bit integers, and the interpreter knows nothing about
it.  Adding a cache of _any_ kind (LRU or otherwise) would make it
even slower (in the application, there's no reason to expect that x -
x_base will repeat a value before O(sqrt(n)) iterations, which itself
can be thousands of bits - a cache hit would be a miracle).