hashing an array - howto

[sudhi.herle at gmail.com]

On Sep 5, 9:38 am, Helmut Jarausch <jarau... at skynet.be> wrote:
> Hi,
>
> I need to hash arrays of integers (from the hash module).
>
> So, I have to derive from array and supply a __hash__ method.

I don't believe you need to derive from an array.

Here are two simple and well known hash functions you can use readily:

def djbhash(a):
    """Hash function from D J Bernstein"""

    h = 5381L
    for i in a:
        t = (h * 33) & 0xffffffffL
        h = t ^ i

    return h


def fnvhash(a):
    """Fowler, Noll, Vo Hash function"""
    h = 2166136261
    for i in a:
        t = (h * 16777619) & 0xffffffffL
        h = t ^ i

    return h

if __name__ == '__main__':
    arr = [1001, 3001, 5001, 9001, 10011, 10013, 10015, 10017, 10019,
20011, 23001]
    print djbhash(arr)
    print fnvhash(arr)


And finally, here is an excellent page that explains hash functions:
   http://eternallyconfuzzled.com/tuts/algorithms/jsw_tut_hashing.aspx

Here is Noll's page where he explains the FNV Hash:
   http://www.isthe.com/chongo/tech/comp/fnv/

Hope this helps,
--
Sudhi