Python implementation of Jenkins Hash?

Question

Does there exist a native Python implementation of the Jenkins hash algorithm(s)?

I need a hash algorithm that takes an arbitrary string and turns it into an 32-bit integer. For a given string, it must guarantee to return the same integer across platforms.

I have looked at the ELF hash algorithm, of which I have found a Python implementation. Could this be a suitable replacement given the above criteria? (http://www.partow.net/programming/hashfunctions/#ELFHashFunction)

Answer 1

There is already a "jenkins" package on PyPi. But it is not "native" as the core implementation is in C.

Answer 2

You can just use the first 32 bits of an md5sum

>>> from hashlib import md5
>>> from struct import unpack
>>> unpack("<IIII",md5("thestring").digest())[0]
1515985217

Answer 3

Ended up implementing it on my own. Released according to the original copyright notice (see below). Use at your own risk and have fun :-)

'''Implements a straight Jenkins lookup hash - http://burtleburtle.net/bob/hash/doobs.html

Usage: 
    from jhash import jhash
    print jhash('My hovercraft is full of eels')

Returns: unsigned 32 bit integer value

Prereqs: None

Tested with Python 2.6.
Version 1.00 - [email protected] - 23.08.2010

Partly based on the Perl module Digest::JHash
http://search.cpan.org/~shlomif/Digest-JHash-0.06/lib/Digest/JHash.pm

Original copyright notice:
    By Bob Jenkins, 1996.  [email protected].  You may use this
    code any way you wish, private, educational, or commercial.  It's free.

    See http://burtleburtle.net/bob/hash/evahash.html
    Use for hash table lookup, or anything where one collision in 2^^32 is
    acceptable.  Do NOT use for cryptographic purposes.
'''

def mix(a, b, c):
    '''mix() -- mix 3 32-bit values reversibly.
For every delta with one or two bits set, and the deltas of all three
  high bits or all three low bits, whether the original value of a,b,c
  is almost all zero or is uniformly distributed,
* If mix() is run forward or backward, at least 32 bits in a,b,c
  have at least 1/4 probability of changing.
* If mix() is run forward, every bit of c will change between 1/3 and
  2/3 of the time.  (Well, 22/100 and 78/100 for some 2-bit deltas.)'''
    # Need to constrain U32 to only 32 bits using the & 0xffffffff 
    # since Python has no native notion of integers limited to 32 bit
    # http://docs.python.org/library/stdtypes.html#numeric-types-int-float-long-complex
    a &= 0xffffffff; b &= 0xffffffff; c &= 0xffffffff
    a -= b; a -= c; a ^= (c>>13); a &= 0xffffffff
    b -= c; b -= a; b ^= (a<<8); b &= 0xffffffff
    c -= a; c -= b; c ^= (b>>13); c &= 0xffffffff
    a -= b; a -= c; a ^= (c>>12); a &= 0xffffffff
    b -= c; b -= a; b ^= (a<<16); b &= 0xffffffff
    c -= a; c -= b; c ^= (b>>5); c &= 0xffffffff
    a -= b; a -= c; a ^= (c>>3); a &= 0xffffffff
    b -= c; b -= a; b ^= (a<<10); b &= 0xffffffff
    c -= a; c -= b; c ^= (b>>15); c &= 0xffffffff
    return a, b, c

def jhash(data, initval = 0):
    '''hash() -- hash a variable-length key into a 32-bit value
  data    : the key (the unaligned variable-length array of bytes)
  initval : can be any 4-byte value, defaults to 0
Returns a 32-bit value.  Every bit of the key affects every bit of
the return value.  Every 1-bit and 2-bit delta achieves avalanche.'''
    length = lenpos = len(data)

    # empty string returns 0
    if length == 0:
        return 0

    # Set up the internal state
    a = b = 0x9e3779b9 # the golden ratio; an arbitrary value
    c = initval        # the previous hash value
    p = 0              # string offset

    # ------------------------- handle most of the key in 12 byte chunks
    while lenpos >= 12:
        a += (ord(data[p+0]) + (ord(data[p+1])<<8) + (ord(data[p+2])<<16) + (ord(data[p+3])<<24))
        b += (ord(data[p+4]) + (ord(data[p+5])<<8) + (ord(data[p+6])<<16) + (ord(data[p+7])<<24))
        c += (ord(data[p+8]) + (ord(data[p+9])<<8) + (ord(data[p+10])<<16) + (ord(data[p+11])<<24))
        a, b, c = mix(a, b, c)
        p += 12
        lenpos -= 12

    # ------------------------- handle the last 11 bytes
    c += length
    if lenpos >= 11: c += ord(data[p+10])<<24
    if lenpos >= 10: c += ord(data[p+9])<<16
    if lenpos >= 9:  c += ord(data[p+8])<<8
    # the first byte of c is reserved for the length
    if lenpos >= 8:  b += ord(data[p+7])<<24
    if lenpos >= 7:  b += ord(data[p+6])<<16
    if lenpos >= 6:  b += ord(data[p+5])<<8
    if lenpos >= 5:  b += ord(data[p+4])
    if lenpos >= 4:  a += ord(data[p+3])<<24
    if lenpos >= 3:  a += ord(data[p+2])<<16
    if lenpos >= 2:  a += ord(data[p+1])<<8
    if lenpos >= 1:  a += ord(data[p+0])
    a, b, c = mix(a, b, c)

    # ------------------------- report the result
    return c

if __name__ == "__main__": 
    hashstr = 'My hovercraft is full of eels'
    myhash = jhash(hashstr)
    print 'jhash("%s"): %d' % (hashstr, myhash)