Python日志記錄：在模式“ w”下不工作但在模式“ a”下的FileHandler正常工作

Question

在Windows下的python 2.7.5 ，當FileHandler處於模式'w' （寫入之前截斷文件）時，處理程序不會僅寫入最后一行。 在'a'模式下，一切都很好。

我的logging.conf文件：

[loggers]
keys=root

[handlers]
keys=consoleHandler,fileHandler

[formatters]
keys=simpleFormatter

[logger_root]
level=NOTSET
handlers=fileHandler

[handler_consoleHandler]
class=StreamHandler
level=DEBUG
formatter=simpleFormatter
args=(sys.stdout,)

[handler_fileHandler]
class=FileHandler
level=DEBUG
formatter=simpleFormatter
args=('generator.log', 'a', 'utf8', 0)

[formatter_simpleFormatter]
format=[ %(asctime)s ] [ %(name)s ] [ %(levelname)-5s ] - %(message)s
datefmt=

我的oracle.py文件：

__author__ = 'wbar'
import cx_Oracle
from contextlib import closing
import logging


class Connector(object):
    __connection__ = None
    __user_name__ = None
    __password__ = None
    __tns_name__ = None
    __logger__ = None

    def get_connection(self, auto_connect=True):
        if auto_connect and not self.__connection__:
            self.__logger__.info(u'Connecting into Oracle: %s@%s', self.__user_name__, self.__tns_name__)
            self.__connection__ = cx_Oracle.connect(
                u'%s/%s@%s' % (self.__user_name__, self.__password__, self.__tns_name__))
        return self.__connection__

    def __init__(self, user_name, password, tns_name):
        self.__user_name__ = user_name
        self.__password__ = password
        self.__tns_name__ = tns_name
        self.__logger__ = logging.getLogger('OracleConnector')
        self.__logger__.addHandler(logging.NullHandler())

    def __del__(self):
        self.close_connection()

    def close_connection(self):
        connection = self.get_connection(auto_connect=False)
        if connection:
            self.__logger__.info(u'Closing connection with Oracle: %s@%s', self.__user_name__, self.__tns_name__)
            connection.close()

    def execute(self, sql):
        with closing(self.get_connection().cursor()) as cursor:
            self.__logger__.debug(u'Executing: %s', sql)
            cursor.execute(sql)
            return cursor.fetchall()

最后是我的主文件generator.py ：

__author__ = 'wbar'
import logging
import logging.config

logging.FileHandler
logging.config.fileConfig('logging.conf')

from oracle import Connector as OracleConnector
DATABASE = OracleConnector(user_name=u'foo', password=u'bar', tns_name=u'db_local')

for line in DATABASE.execute('select * from dual'):
    print(line[0])

logger = logging.getLogger('root')

logger.debug('DEBUG')
logger.info('INFO')
logger.error('ERROR')

在'a'模式下，日志文件如下所示：

[ 2013-11-13 17:15:25,608 ] [ OracleConnector ] [ INFO  ] - Connecting into Oracle: pms_test@db_impaq_local
[ 2013-11-13 17:15:25,727 ] [ OracleConnector ] [ DEBUG ] - Executing: select * from dual
[ 2013-11-13 17:15:25,730 ] [ root ] [ DEBUG ] - DEBUG
[ 2013-11-13 17:15:25,730 ] [ root ] [ INFO  ] - INFO
[ 2013-11-13 17:15:25,730 ] [ root ] [ ERROR ] - ERROR
[ 2013-11-13 17:15:25,734 ] [ OracleConnector ] [ INFO  ] - Closing connection with Oracle: pms_test@db_impaq_local

在'w'模式下，日志文件如下所示：

[ 2013-11-13 17:06:24,239 ] [ OracleConnector ] [ INFO  ] - Closing connection with Oracle: pms_test@db_impaq_local

Answer 1

logging模塊注冊一個atexit關閉鈎子，以關閉所有處理程序。 Python退出時，這將關閉打開的'w'文件對象。

然而，你的oracle.Connector()類有一個__del__方法，Python的退出時其也被稱為。 Python在清除全局變量之前調用atexit ，因此此處的確切操作順序為：

1. logging的atexit掛鈎被調用，文件被關閉。
2. oracle.Connector().__del__() ，它調用self.__logger__.info() 。 這將重新打開關閉的文件處理程序以進行日志記錄，從而截斷文件。

為避免這種情況，請在退出Python 之前顯式關閉連接器：

DATABASE.close_connection()