code: def create_id(self, prefix="guid"):
          
          if self.method == IDGenerator.METHOD_UUID:
              id_ = str(uuid.uuid4())
          elif self.method == IDGenerator.METHOD_INT:
              id_ = self.next_int
              self.next_int += 1
          else:
              raise InvalidMethodError(self.method)
  
          return "%s:%s-%s" % (self.namespace.prefix, prefix, id_)
docs: Create an ID.
  
          Note that if `prefix` is not provided, it will be `guid`, even if the
          `method` is `METHOD_INT`.