Question

cur.executemany(sql, rows)

我将rows作为空迭代器，它会触发错误。

如果我cur.executemany(sql, list(rows))，那么它可以正常工作。

 File "/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/MySQLdb/cursors.py", line 252, in executemany
    r = self._query('\n'.join([query[:p], ',\n'.join(q), query[e:]]))
  File "/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/MySQLdb/cursors.py", line 344, in _query
    rowcount = self._do_query(q)
  File "/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/MySQLdb/cursors.py", line 308, in _do_query
    db.query(q)
_mysql_exceptions.ProgrammingError: (1064, "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 1")

以下是MySQLdb Cursors.py

的代码

    def executemany(self, query, args):

        """Execute a multi-row query.

        query -- string, query to execute on server

        args

            Sequence of sequences or mappings, parameters to use with
            query.

        Returns long integer rows affected, if any.

        This method improves performance on multiple-row INSERT and
        REPLACE. Otherwise it is equivalent to looping over args with
        execute().

        """
        del self.messages[:]
        db = self._get_db()
        if not args: return
        if isinstance(query, unicode):
            query = query.encode(db.unicode_literal.charset)
        m = insert_values.search(query)
        if not m:
            r = 0
            for a in args:
                r = r + self.execute(query, a)
            return r
        p = m.start(1)
        e = m.end(1)
        qv = m.group(1)
        try:
            q = [ qv % db.literal(a) for a in args ]
        except TypeError, msg:
            if msg.args[0] in ("not enough arguments for format string",
                               "not all arguments converted"):
                self.errorhandler(self, ProgrammingError, msg.args[0])
            else:
                self.errorhandler(self, TypeError, msg)
        except (SystemExit, KeyboardInterrupt):
            raise
        except:
            exc, value, tb = sys.exc_info()
            del tb
            self.errorhandler(self, exc, value)
        r = self._query('\n'.join([query[:p], ',\n'.join(q), query[e:]]))
        if not self._defer_warnings: self._warning_check()
        return r

Answer 1

简短的回答是：不，MySQLdb不支持将空迭代器参数传递给executemany。

为什么不呢？由于行if not args: return。这将处理通过完全切断服务器并返回None而不提供参数的情况。空列表，字典，集合或元组的真值是False，但迭代器的真值始终为True。

如果在cursors.py中注释掉该行，那么任何空序列或映射都会抛出与空迭代器相同的ER_PARSE_ERROR。

为了让executemany支持空参数，它必须以某种方式测试args是否为空。如果args是迭代器，那么执行此操作的唯一方法是调用.next()并观察结果是否为StopIteration异常;没有其他方法可以确定任意迭代器是否为空。这是不切实际的，因为它从迭代器中消耗了一个项目，并且不适用于任何非迭代器类型，并且没有意义，因为executemany不打算在没有参数的情况下使用。

MySQLdb游标不支持空迭代器吗？

1 个答案: