Python MySQLdb 转换器不工作

Question

我正在尝试使用 python 和 MySQLdb 运行 ETL 脚本，但我对初始提取查询的结果感到困惑。当我想要 Int 和 Float 时，返回的类型都是 Long 和 Decimal。我已经搜索了几个小时，试图找到这个问题的答案，但没有成功。

database = MySQLdb.connect(host='db',user='user',
                       passwd='password', db='db123')

database_cursor = database.cursor()

database_query = ("SELECT id, siteId, campaignId, hour, sum(impressions) AS impressions, "
"sum(clicks) AS clicks, sum(conversions) AS conversions, sum(costs/1000000) AS revenue "
"FROM database.DM_PublisherFact_Hourly WHERE time = '%s' GROUP BY siteId, campaignId;") %(today)

print database_query

database_cursor.execute(database_query)
result = database_cursor.fetchone()

database.close()

返回值是 Longs 和 Decimals 的元组。我尝试将转换字典显式传递给连接对象，但没有成功。有帮助吗？

这是转换代码

"""MySQLdb type conversion module

This module handles all the type conversions for MySQL. If the default
type conversions aren't what you need, you can make your own. The
dictionary conversions maps some kind of type to a conversion function
which returns the corresponding value:

Key: FIELD_TYPE.* (from MySQLdb.constants)

Conversion function:

Arguments: string

Returns: Python object

Key: Python type object (from types) or class

Conversion function:

Arguments: Python object of indicated type or class AND 
           conversion dictionary

Returns: SQL literal value

Notes: Most conversion functions can ignore the dictionary, but
       it is a required parameter. It is necessary for converting
       things like sequences and instances.

Don't modify conversions if you can avoid it. Instead, make copies
(with the copy() method), modify the copies, and then pass them to
MySQL.connect().

"""

from _mysql import string_literal, escape_sequence, escape_dict, escape, NULL
from constants import FIELD_TYPE, FLAG
from times import *
import types
import array

try:
set
except NameError:
from sets import Set as set

def Bool2Str(s, d): return str(int(s))

def Str2Set(s):
values = s.split(',')
return map(str, tuple(values))

def Set2Str(s, d):
return string_literal(','.join(s), d)

def Thing2Str(s, d):
"""Convert something into a string via str()."""
return str(s)

def Unicode2Str(s, d):
"""Convert a unicode object to a string using the default encoding.
This is only used as a placeholder for the real function, which
is connection-dependent."""
return s.encode()

Long2Int = Thing2Str

def Float2Str(o, d):
return '%.15g' % o

def None2NULL(o, d):
"""Convert None to NULL."""
return NULL # duh

def Thing2Literal(o, d):

"""Convert something into a SQL string literal.  If using
MySQL-3.23 or newer, string_literal() is a method of the
_mysql.MYSQL object, and this function will be overridden with
that method when the connection is created."""

return string_literal(o, d)


def Instance2Str(o, d):

"""

Convert an Instance to a string representation.  If the __str__()
method produces acceptable output, then you don't need to add the
class to conversions; it will be handled by the default
converter. If the exact class is not found in d, it will use the
first class it can find for which o is an instance.

"""

if d.has_key(o.__class__):
    return d[o.__class__](o, d)
cl = filter(lambda x,o=o:
            type(x) is types.ClassType
            and isinstance(o, x), d.keys())
if not cl and hasattr(types, 'ObjectType'):
    cl = filter(lambda x,o=o:
                type(x) is types.TypeType
                and isinstance(o, x)
                and d[x] is not Instance2Str,
                d.keys())
if not cl:
    return d[types.StringType](o,d)
d[o.__class__] = d[cl[0]]
return d[cl[0]](o, d)

def char_array(s):
return array.array('c', s)

def array2Str(o, d):
return Thing2Literal(o.tostring(), d)

conversions = {
types.IntType: Thing2Str,
types.LongType: Long2Int,
types.FloatType: Float2Str,
types.NoneType: None2NULL,
types.TupleType: escape_sequence,
types.ListType: escape_sequence,
types.DictType: escape_dict,
types.InstanceType: Instance2Str,
array.ArrayType: array2Str,
types.StringType: Thing2Literal, # default
types.UnicodeType: Unicode2Str,
types.ObjectType: Instance2Str,
types.BooleanType: Bool2Str,
DateTimeType: DateTime2literal,
DateTimeDeltaType: DateTimeDelta2literal,
set: Set2Str,
FIELD_TYPE.TINY: int,
FIELD_TYPE.SHORT: int,
FIELD_TYPE.LONG: long,
FIELD_TYPE.FLOAT: float,
FIELD_TYPE.DOUBLE: float,
FIELD_TYPE.DECIMAL: float,
FIELD_TYPE.NEWDECIMAL: float,
FIELD_TYPE.LONGLONG: long,
FIELD_TYPE.INT24: int,
FIELD_TYPE.YEAR: int,
FIELD_TYPE.SET: Str2Set,
FIELD_TYPE.TIMESTAMP: mysql_timestamp_converter,
FIELD_TYPE.DATETIME: DateTime_or_None,
FIELD_TYPE.TIME: TimeDelta_or_None,
FIELD_TYPE.DATE: Date_or_None,
FIELD_TYPE.BLOB: [
    (FLAG.BINARY, str),
    ],
FIELD_TYPE.STRING: [
    (FLAG.BINARY, str),
    ],
FIELD_TYPE.VAR_STRING: [
    (FLAG.BINARY, str),
    ],
FIELD_TYPE.VARCHAR: [
    (FLAG.BINARY, str),
    ],
}

try:
from decimal import Decimal
conversions[FIELD_TYPE.DECIMAL] = Decimal
conversions[FIELD_TYPE.NEWDECIMAL] = Decimal
except ImportError:
pass

try:
from types import BooleanType
def Bool2Str(s, d): return str(int(s))
conversions[BooleanType] = Bool2Str
except ImportError:
pass

Answer 1

您的转换字典需要使用 MySQL 类型作为键，而不是 Python 类型:

import _mysql  
from MySQLdb.constants import FIELD_TYPE
my_conv = { FIELD_TYPE.LONG: int }
db=_mysql.connect(conv=my_con)

来自 http://mysql-python.sourceforge.net/MySQLdb.html

看来您需要使用 _mysql.connect() 而不是 MySQLdb.connect() 才能使用转换。