code: def add_choice(self, choice_name):
          
  
          if not ALLOWED_NAMES.match(choice_name):
              raise ExperimentException(self.name, "Illegal choice name: %s" % choice_name)
  
          if choice_name in self.choice_names:
              raise ExperimentException(self.name, "Choice already exists: %s" % choice_name)
  
          self.choice_names.append(choice_name)
          self.redis.hset(EXPERIMENT_REDIS_KEY_TEMPLATE % self.name, "choices", escape.json_encode(self.choice_names))
          self.refresh()
docs: Adds a choice for the experiment