python mysqldb 游标消息列表错误显示两次

Question

不知道为什么，每次我在数据库游标上运行查询时，它的 .messages 列表里都会生成两个错误，这算不算一种特性呢？

下面是运行查询的代码，整个应用程序的工作就是打开一个与数据库的连接，强制产生一个错误后运行这个查询，读取 .messages，然后退出。

import MySQLdb

class dbobject:
    def __init__(self, dbhost, dbuser, dbpass, dbname):
        self.connection = MySQLdb.connect( user=dbuser, passwd=dbpass, host=dbhost, db=dbname )
        self.cursor = self.connection.cursor()

    def try_query(self, query, args=()):
        """ attempts to run a query, where
                query is the query to be run, with '%s' statements where the values should be, and
                args is a tuple of the values to go with the query"""
        try:
            if args == ():
                self.cursor.execute(query)
            else:
                self.cursor.execute(query, args)
            self.connection.commit()
        except:

            self.connection.rollback()

    def add_unit(self, name, version, credits):
        """ takes name, version, credits
                name is the name of the unit paper
                version is the unit version, and
                credits is how many credits its worth"""
        self.try_query("insert into dsfdf tbl_unit (unit_name, unit_version, unit_credits) values (%s,%s,%s)",(name,version,credits))

    def close(self):
        self.cursor.close()
        self.connection.close()


blah = dbobject(#####################)
blah.add_unit( "thing", "something", 6)
for i in blah.cursor.messages:
    print i
blah.close()

Answer 1

也许你可以把你收到的消息发出来。

mysql_insert_etc.py:22: 警告：数据在第1行的'val'列被截断
self.cursor.execute(query, args) (, ('警告', 1265L, "数据在第1行的'val'列被截断"))

从上面的（制造的错误）来看，MySQLdb 返回了：

1. MySQL 的警告，和
2. 它自己的异常。

使用下面的代码，你可以选择要么抑制警告，要么让它们引发异常。

引发异常（稍微修改自 这个例子）：

from warnings import catch_warnings, simplefilter

def try_query(self, query, args=()):
    with catch_warnings():
        simplefilter('error', MySQLdb.Warning)
        try:
            if args == ():
                self.cursor.execute(query)
            else:
                self.cursor.execute(query, args)
            self.connection.commit()
        except MySQLdb.Error, e:
            self.connection.rollback()
            raise e

抑制警告（来自这里）：

from warnings import filterwarnings

filterwarnings('ignore', category=MySQLdb.Warning)