构建查询字符串时的Python TypeError

Question

我正在构建一个查询字符串.

query = "SELECT seqid, date, name, steamid, team, text, type, '%s' as triggerword, '%s' as weight FROM chatlogs WHERE date > '%s' AND text LIKE '%%%s%%' ORDER BY DATE" % (word, weight, self.setting['LAST_RUN_TIME'], word)

如果我打印字符串,它会正确返回:

SELECT seqid, date, name, steamid, team, text, type, 'hunting_term' as triggerword, '0.01' as weight FROM chatlogs WHERE date > '2012-04-18 23:47:58.439124' AND text LIKE '%hunting_term%' ORDER BY DATE

但是,它会因TypeError异常而失败:TypeError:格式字符串的参数不足

完整代码:

import database

mysqldb = database.Connection('localhost','mydb',user='myuser',password='mypass')

word = 'hunting_term'
weight = 0.01
setting = dict({'LAST_RUN_TIME':'2012-04-18 23:47:58.439124'})

query = "SELECT seqid, date, name, steamid, team, text, type, '%s' as triggerword, '%s' as weight FROM chatlogs WHERE date > '%s' AND text LIKE '%%%s%%' ORDER BY DATE" % (word, weight, setting['LAST_RUN_TIME'], word)
print query

for message in mysqldb.query(query):        # This is the line it throws the exception on
    print "A row"

数据库来自龙卷风包

Answer 1

这里的问题是最终调用MySQLdb看起来像这样:

query = "SELECT seqid, date, name, steamid, team, text, type, 'hunting_term' as triggerword, '0.01' as weight FROM chatlogs WHERE date > '2012-04-18 23:47:58.439124' AND text LIKE '%hunting_term%' ORDER BY DATE"
db.cursor().execute(query, ())

第一个参数db.cursor().execute()应该是格式字符串,第二个参数应该是该格式字符串的替换,您可以在MySQLdb文档中看到这一点.换句话说,它将执行以下代码:

query % ()

如您所见,这将导致相同的TypeError:

>>> query % ()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: not enough arguments for format string

这意味着%您希望MySQL看到的任何文字都需要在看到%%它时db.cursor().execute(),因此您应该能够通过将原始格式字符串更改为以下内容来解决此问题:

query = "SELECT seqid, date, name, steamid, team, text, type, '%s' as triggerword, '%s' as weight FROM chatlogs WHERE date > '%s' AND text LIKE '%%%%%s%%%%' ORDER BY DATE" % (word, weight, self.setting['LAST_RUN_TIME'], word)

但是,正确的方法是让MySQLdb为您执行替换,这会将您的代码更改为以下内容:

query = "SELECT seqid, date, name, steamid, team, text, type, %s as triggerword, %s as weight FROM chatlogs WHERE date > %s AND text LIKE %s ORDER BY DATE"
parameters = (word, weight, setting['LAST_RUN_TIME'], '%%%s%%' % word)
for message in mysqldb.query(query, *parameters):
    print "A row"