mysql-python:not all arguments converted during string formatting

今天把django从1.5.5升级到了1.6.2，结果使用mysql-python查询数据库时候就报了这个错误：“not all arguments converted during string formatting”

貌似这个问题应该和django没什么关系，正好今天就看看mysql-python的源码吧。想看如何解决的请直接跳到最后。

查询部分简化后如下：

posistion = "top"
order = r"select id,p_name,p_explain,p_href from pictures where p_position = %s and p_show = 1 order by -id"
self.cur.execute(order, position)

mysql-python中execute函数：

def execute(self, query, args=None):
        """Execute a query.
        query -- string, query to execute on server
        args -- optional sequence or mapping, parameters to use with query.
        Note: If args is a sequence, then %s must be used as the
        parameter placeholder in the query. If a mapping is used,
        %(key)s must be used as the placeholder.
        Returns long integer rows affected, if any
        """
        del self.messages[:]
        db = self._get_db()
        if isinstance(query, unicode):
            query = query.encode(db.unicode_literal.charset)
        if args is not None:
            if isinstance(args, dict):
                query = query % dict((key, db.literal(item))
                                     for key, item in args.iteritems())
            else:
                query = query % tuple([db.literal(item) for item in args]) ##########################这里！！
        try:
            r = None
            r = self._query(query)
        except TypeError, m:
            if m.args[0] in ("not enough arguments for format string",
                             "not all arguments converted"):
                self.messages.append((ProgrammingError, m.args[0]))
                self.errorhandler(self, ProgrammingError, m.args[0])
            else:
                self.messages.append((TypeError, m))
                self.errorhandler(self, TypeError, m)
        except (SystemExit, KeyboardInterrupt):
            raise
        except:
            exc, value, tb = sys.exc_info()
            del tb
            self.messages.append((exc, value))
            self.errorhandler(self, exc, value)
        self._executed = query
        if not self._defer_warnings: self._warning_check()
        return r

错误地方就是后面加了#的语句。

可以看到，因为字符串也是可序列化的，所以一个字符串被拆分成了单个的字符进行db.literal()处理。这个db是什么呢？

往上找：

def __init__(self, connection):
        from weakref import proxy
        self.connection = proxy(connection)
        self.description = None
        self.description_flags = None
        self.rowcount = -1
        self.arraysize = 1
        self._executed = None
        self.lastrowid = None
        self.messages = []
        self.errorhandler = connection.errorhandler
        self._result = None
        self._warnings = 0
        self._info = None
        self.rownumber = None
    def _get_db(self):
        if not self.connection:
            self.errorhandler(self, ProgrammingError, "cursor closed")
        return self.connection
```        
可以看出，这个db就是connection的一个弱引用。再进一步，这个connnection哪来的呢？

```python
def open(self):
    """ 返回一个默认的数据库连接游标 """
    try:
        self.conn = MySQLdb.Connection(
            self.db_ip,
            self.db_un,
            self.db_pd,
            self.db_db,
            charset=self.db_ch)
        self.cur = self.conn.cursor()
    except MySQLdb.Error as e:
        print e
`

mysqldb-python的connection.py中:

class Connection(_mysql.connection):
    """MySQL Database Connection Object"""
    default_cursor = cursors.Cursor

那这个Cursor又是什么呢？

class Cursor(CursorStoreResultMixIn, CursorTupleRowsMixIn,
             BaseCursor):
    """This is the standard Cursor class that returns rows as tuples
    and stores the result set in the client."""

这个Cursor这些类的子类，其中最上面出错函数就是BaseCursor的一个方法。

有点跑偏，先看看那literal函数吧：

def literal(self, o):
        print o,type(o)
        print self.encoders
        """
        If o is a single object, returns an SQL literal as a string.
        If o is a non-string sequence, the items of the sequence are
        converted and returned as a sequence.
        Non-standard. For internal use; do not use this in your
        applications.
        """
        return self.escape(o, self.encoders)

print是我添加的，输出如下：

t <type 'str'>
{<type 'instance'>: <function Instance2Str at 0x17b3aa0>, <type 'set'>: <function Set2Str at 0x17b3cf8>, <type 'long'>: <function Thing2Str at 0x17b3de8>, <type 'bool'>: <function Bool2Str at 0x17b3ed8>, <type 'unicode'>: <function unicode_literal at 0x7f12e42c4230>, <type 'str'>: <function string_literal at 0x7f12e42be2a8>, <type 'float'>: <function Float2Str at 0x17b3c08>, <type 'list'>: <function quote_tuple at 0x17b3938>, <type 'tuple'>: <function quote_tuple at 0x17b3938>, <type 'array.array'>: <function array2Str at 0x17b39b0>, <type 'NoneType'>: <function None2NULL at 0x17b3b90>, <type 'datetime.datetime'>: <function DateTime2literal at 0x17b30c8>, <type 'dict'>: <built-in function escape_dict>, <type 'object'>: <function Instance2Str at 0x17b3aa0>, <type 'int'>: <function Thing2Str at 0x17b3de8>, <type 'datetime.timedelta'>: <function DateTimeDelta2literal at 0x17b3140>}
o <type 'str'>
{<type 'instance'>: <function Instance2Str at 0x17b3aa0>, <type 'set'>: <function Set2Str at 0x17b3cf8>, <type 'long'>: <function Thing2Str at 0x17b3de8>, <type 'bool'>: <function Bool2Str at 0x17b3ed8>, <type 'unicode'>: <function unicode_literal at 0x7f12e42c4230>, <type 'str'>: <function string_literal at 0x7f12e42be2a8>, <type 'float'>: <function Float2Str at 0x17b3c08>, <type 'list'>: <function quote_tuple at 0x17b3938>, <type 'tuple'>: <function quote_tuple at 0x17b3938>, <type 'array.array'>: <function array2Str at 0x17b39b0>, <type 'NoneType'>: <function None2NULL at 0x17b3b90>, <type 'datetime.datetime'>: <function DateTime2literal at 0x17b30c8>, <type 'dict'>: <built-in function escape_dict>, <type 'object'>: <function Instance2Str at 0x17b3aa0>, <type 'int'>: <function Thing2Str at 0x17b3de8>, <type 'datetime.timedelta'>: <function DateTimeDelta2literal at 0x17b3140>}
p <type 'str'>
{<type 'instance'>: <function Instance2Str at 0x17b3aa0>, <type 'set'>: <function Set2Str at 0x17b3cf8>, <type 'long'>: <function Thing2Str at 0x17b3de8>, <type 'bool'>: <function Bool2Str at 0x17b3ed8>, <type 'unicode'>: <function unicode_literal at 0x7f12e42c4230>, <type 'str'>: <function string_literal at 0x7f12e42be2a8>, <type 'float'>: <function Float2Str at 0x17b3c08>, <type 'list'>: <function quote_tuple at 0x17b3938>, <type 'tuple'>: <function quote_tuple at 0x17b3938>, <type 'array.array'>: <function array2Str at 0x17b39b0>, <type 'NoneType'>: <function None2NULL at 0x17b3b90>, <type 'datetime.datetime'>: <function DateTime2literal at 0x17b30c8>, <type 'dict'>: <built-in function escape_dict>, <type 'object'>: <function Instance2Str at 0x17b3aa0>, <type 'int'>: <function Thing2Str at 0x17b3de8>, <type 'datetime.timedelta'>: <function DateTimeDelta2literal at 0x17b3140>}

就像上面说的，”top”被拆分成了3个，可是我们语句中的占位符%s只有一个！所以报错 not all arguments converted during string formatting。最初这里我理解成了是哪里转化出了错误，最后醒悟这意思是因为占位符个数和传入参数个数不一样导致！英语不过关阿～不过以前怎么没报错呢？？奇怪……

解决办法有2个，简单的方法就是执行语句修改如下：self.cur.execute(order, (position,)) #注意逗号。

更推荐的方法就是使用字典传值：

if show:
    order = r"select id,p_name,p_explain,p_href from pictures where p_position = %(position)s and p_show = 1 order by -id"
else:
    order = r"select id,p_name,p_explain,p_href,p_uploaddate,p_show from pictures where p_position = %(position)s"
self.cur.execute(order, {'position': position})

这样虽然多打了几个字母，不过却是一种最稳妥的方式，不用担心由于参数顺序造成错误了。

mysql-python源码写的狠帅阿!