code: def registerNamespaceAlias(namespace_uri, alias):
      
      global registered_aliases
  
      if registered_aliases.get(alias) == namespace_uri:
          return
  
      if namespace_uri in list(registered_aliases.values()):
          raise NamespaceAliasRegistrationError(
              'Namespace uri %r already registered' % (namespace_uri, ))
  
      if alias in registered_aliases:
          raise NamespaceAliasRegistrationError('Alias %r already registered' %
                                                (alias, ))
  
      registered_aliases[alias] = namespace_uri
docs: Registers a (namespace URI, alias) mapping in a global namespace
      alias map.  Raises NamespaceAliasRegistrationError if either the
      namespace URI or alias has already been registered with a
      different value.  This function is required if you want to use a
      namespace with an OpenID 1 message.