[Python-Dev] Why not using the hash when comparing strings?

[Benjamin Peterson]

2012/10/18 Victor Stinner <victor.stinner at gmail.com>:
> Hi,
>
> I would like to know if there a reason for not using the hash of
> (bytes or unicode) strings when comparing two objects and the hash of
> the two objects was already been computed. Using the hash would speed
> up comparaison of long strings when the two strings are different.
>
> Something like:
>
>     if ((op == Py_EQ || op == Py_NE)
>         && a->ob_shash != -1
>         && b->ob_shash != -1
>         && a->ob_shash != b->ob_shash) {
>         /* strings are not equal */
>     }
>
> There are hash collision, so a->ob_shash == b->ob_shash doesn't mean
> that the two strings are equal. But if the two hashs are different,
> the two strings are different. Isn't it?

It would be interesting to see how common it is for strings which have
their hash computed to be compared.



-- 
Regards,
Benjamin