Python和MySQLdb-使用DROP TABLE IF EXISTS似乎会引发异常 [英] Python and MySQLdb - Using DROP TABLE IF EXISTS seems to throw exception

问题描述

我收到了此代码.

.....
try:
    task_db.cursor.execute('DROP TABLE IF EXISTS `tasks`')
    print "Affected: %d" % task_db.cursor.rowcount 
except MySQLdb.Error, e:
    print "Error ocurred: %s " % e.args[0]
    print e

如果任务表不存在，则会收到类似

If the tasks table doesn't exist, then I get a warning like

create_database.py:11: Warning: Unknown table 'tasks'

但是如果表确实存在，那么我将不会收到该警告. 奇怪吗?

But if the table does exist then I wont get that warning. Odd?

推荐答案

这是完全正确的行为.如果该表存在，则将其删除.如果它不存在，那么您会得到警告异常，该异常与 Error 不同-您可以随意忽略它，也不会发生任何不良情况，但是您必须抓住它可以让您的脚本继续执行.

It's perfectly correct behaviour. If the table exists, then it's dropped. If it doesn't exist then you get Warning exception which is not the same as Error - you are free to ignore it and nothing bad should happen, but you have to catch it to allow your script to proceed.

要防止警告冒泡，只需将其作为其他任何异常捕获即可:

To prevent Warning from bubbling up, just catch it as any other exception:

try:
    [some code]
except MySQLdb.Warning:
    [exception handling code]

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