'Takes something like
field="3,79159750" and returns 7 as the index'

def get_key(self, field):

    import hashlib
    field = str(field).encode('utf-8')
    number = int(hashlib.md5(field).hexdigest(), 16)
    position = (number % self.number_of_keys)
    return (self.key + (':%s' % position))
