code: def getKey(self, namespace, ns_key):
          
          namespace = self._fixNS(namespace)
          if namespace == BARE_NS:
              return ns_key
  
          ns_alias = self.namespaces.getAlias(namespace)
  
          # No alias is defined, so no key can exist
          if ns_alias is None:
              return None
  
          if ns_alias == NULL_NAMESPACE:
              tail = ns_key
          else:
              tail = '%s.%s' % (ns_alias, ns_key)
  
          return 'openid.' + tail
docs: Get the key for a particular namespaced argument