Provide access to the complete hash string.

        The hash string may have zero or more hash values with
        appropriate prefixes. All hash values are assumed to be
        strings

def hash(self):
        """Provide access to the complete hash string.

        The hash string may have zero or more hash values with
        appropriate prefixes. All hash values are assumed to be
        strings
        """
        hashvals = []
        if (self.md5 is not None):
            hashvals.append('md5:' + self.md5)
        if (self.sha1 is not None):
            hashvals.append('sha-1:' + self.sha1)
        if (self.sha256 is not None):
            hashvals.append('sha-256:' + self.sha256)
        if (len(hashvals) > 0):
            return(' '.join(hashvals))
        return(None)