code: def toArgs(self):
          
          # FIXME - undocumented exception
          post_args = self.toPostArgs()
          kvargs = {}
          for k, v in post_args.items():
              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
docs: Return all namespaced arguments, failing if any
          non-namespaced arguments exist.