'Return all namespaced arguments, failing if any
non-namespaced arguments exist.'

def toArgs(self):

    post_args = self.toPostArgs()
    kvargs = {}
    for (k, v) in post_args.iteritems():
        if (not k.startswith('openid.')):
            raise ValueError('This    message    can    only    be    encoded    as    a    POST,    because    it    contains    arguments    that    are    not    prefixed    with    "openid."')
        else:
            kvargs[k[7:]] = v
    return kvargs
