Python 如何检查GQL对象是否为空

我试图检查GQL对象是否为空（在使用Python的Google App Engine中），我应该如何做？ 我试过了，但没用：

comments = db.GqlQuery("SELECT * "
                                "FROM Comment "
                                "where ANCESTOR IS :1 "
                                "order by date DESC", 
                                movie_data) 
        if comments:
            ratingsum = 0
            i=0
            for comment in comments:
                ratingsum=ratingsum + comment.rating
                i+=1
            average = ratingsum/i
        else:
            average = "no ratings"

---

Gql查询提供一个查询对象，但不提供结果（实体）。要获取结果，您必须获取结果：使用fetch、count、get或迭代结果集。

调用

count

需要执行两次相同的查询。因此，为了避免这种情况，并且由于您必须遍历注释，您还可以通过观察一个副作用来“检测”注释何时为空——如果

注释为空，则
i
将为零：

comments = db.GqlQuery("SELECT * "
                                "FROM Comment "
                                "where ANCESTOR IS :1 "
                                "order by date DESC", 
                                movie_data) 
ratingsum = 0
i = 0
for comment in comments:
    ratingsum += comment.rating
    i += 1
if i:    
    average = ratingsum/i
else:    
    average = "no ratings"