Use elements from this hash set to create a unique
        (re)identifier.

def guid(self):
        '''
        Use elements from this hash set to create a unique
        (re)identifier.
        '''
        iden = hashlib.md5()
        props = {'size': self.size}

        for name, item in self.hashes:
            iden.update(item.digest())
            props[name] = item.hexdigest()

        return iden.hexdigest(), props