[Python-Dev] Why not using the hash when comparing strings? (original) (raw)

Steven D'Aprano steve at pearwood.info
Fri Oct 19 03:07:17 CEST 2012

On 19/10/12 12:03, Victor Stinner wrote:

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.

Assuming the hash has already been compared, then I imagine it would be faster.

Something like:

if ((op == PyEQ || op == PyNE) && a->obshash != -1 && b->obshash != -1 && a->obshash != b->obshash) { /* strings are not equal */ } There are hash collision, so a->obshash == b->obshash doesn't mean that the two strings are equal. But if the two hashs are different, the two strings are different. Isn't it?

I would certainly hope so :)

-- Steven

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