在Python For循环中清除元组

Question

在从数据库中读取数据之后，我很难弄清楚如何清除元组“数据”。

流程：

每隔X分钟，我就打电话给batchUpdate

batchUpdate提取符合特定条件的记录

我们遍历那些执行更新的记录。

进程结束并等待下一次调用。

发行：

每次对函数batchUpdate的后续调用都不会产生新的数据。元组'data‘包含与以前相同的值。

简化的示例(每1秒只提取一条记录)：

Update has started
((10938L, u"@anonymized @anonymized House of Cards will be nothing compared  to the Drumpf's!And worst of all is that Americans chose him as president?", u'New York, USA'),)
Update has started
((10938L, u"@anonymized @anonymized House of Cards will be nothing compared to the Drumpf's!And worst of all is that Americans chose him as president?", u'New York, USA'),)
Update has started
((10938L, u"@anonymized @anonymized House of Cards will be nothing compared to the Drumpf's!And worst of all is that Americans chose him as president?", u'New York, USA'),)
Update has started
((10938L, u"@anonymized @anonymized House of Cards will be nothing compared to the Drumpf's!And worst of all is that Americans chose him as president?", u'New York, USA'),)

代码：

class analyzeRecords():
    def batchUpdate(self):

     global data

     #Select up to 1 record

     b.execute(""" SELECT id, tweet,tweet_location_guess FROM rawTweets where compoundScore IS NULL LIMIT 0,1 """)

     #Put that data into a tuple

     data = b.fetchall()

     print(data)

     #print that update has started

     print("Update has started")

     for row in data:
          idMatch = row[0]
          cleanTweet = reduce(lambda x, y: x.replace(y, d[y]), sorted(d, key=lambda i: len(i), reverse=True), row[1].lower())
          sentimentScores = analyzer.polarity_scores(cleanTweet)
          overallScore = sentimentScores["compound"]

          u.execute("""UPDATE rawTweets SET tweet=%s, compoundScore=%s where id=%s""",
                    (cleanTweet, overallScore, idMatch))
          update.commit()

l = task.LoopingCall(analyzeRecords().batchUpdate)
l.start(timeout) # call every sixty seconds

reactor.run()       

Answer 1

在您的代码中，您将执行以下两行：

 global data

 data = b.fetchall()

综合起来，这两个语句应该覆盖以前data变量中的任何内容。

我要指出的是，这个函数似乎不需要全局变量--您可以而且很可能应该为此使用一个局部变量。

无论如何，我不认为问题是存在一些神秘的剩余数据，除非定义了b.fetchall()对象。(例如，如果查询中有错误，或者查询没有返回匹配项，那么它是如何传递的？如果它引发或返回一个您忽略的值，也许fetchall会返回陈旧的数据，因为您应该检查该值，而不是调用fetchall.)

我建议您看看execute和fetchall是如何一起工作的，还可以看看您的for循环。我看到了b.execute，u.execute和update.commit。似乎您有许多不同的数据库连接。也许你知道。或者，您可以复制/粘贴代码，您确实应该这样做：

u.execute(...)
u.commit()