Question

我是Python的新手并且已经开始编写我的第一个模块，它将执行备份到外部存储（通常是一个或多个USB磁盘）。

理想的行为是：

检查是否已安装目标（备份磁盘）。 destination_was_mounted变为True或False
如果destination_was_mounted = False，则安装目的地。
如果mountDestination失败，则引发异常并重新启动循环。
如果mountDestination正常，请检查目标上是否存在checkfile（和backup_dir）。
如果check_destination失败，则引发异常并重新启动循环。
继续处理（尚未编码）。
在任何情况下，如果destination_was_mounted = False，则取消安装目的地。

问题在于，如果check_destination部分引发异常，则即使我在finally部分中有该目的，也无法卸载目标。这就好像destination_was_mounted变为True，即使它应该是假的。或者好像check_destination在mount_destination之前运行，即使它在它之后。

我的参考资料（在查看python文档和我的学习Python书籍中）：

Python: How to tell the for loop to continue from a function?

How to retry after exception in python?

How to get back to the for loop after exception handling

#!/usr/bin/env python3.1

import sys
import os
import os.path
import subprocess
import configparser
CONFIGFILE = 'backup.ini'
# do i need this?
config = {}

config = configparser.ConfigParser()
config.read(CONFIGFILE)
backup_sources = sorted(config.sections()[1:])

class NoCheckFile(Exception):
    pass

def mountDestination(destination):
    return subprocess.check_call(['mount', destination])

def unMountDestination(destination):
    return subprocess.check_call(['umount', destination])

def checkDestination(destination, backup_dir, checkfile):
    return os.path.exists(destination + '/' + backup_dir + '/' + checkfile)

''' exception handlers '''
# perhaps add another arg like 0 or 1 for success/failure
def handleCalledProcessError(ex):
    print('Exception: ' + str(ex))

def handleNoCheckFile(ex):
    print('Exception: ' + str(ex))

# rename me once I work out logging
def logExecute(result):
    print('Info: ' + str(result))
# can I pass logging output here

def main():
    for section in backup_sources:
        item = dict(config.items(section))
        destination = item['destination']
        destination_was_mounted = os.path.ismount(destination)
        backup_dir = item['backup_dir']
        checkfile = item['checkfile']
        try:
            ''' check destination_was_mounted and mount destination if required '''
            mount_destination = None
            unmount_destination = None
            if not destination_was_mounted:
                mount_destination = mountDestination(destination)

            ''' check that checkfile exists in backup_dir '''
            check_destination = checkDestination(destination, backup_dir, checkfile)
            if not check_destination:
                raise NoCheckFile('no checkfile found')

            ''' lvm snapshot, mount and source path update '''

            ''' backup engine code here '''

            ''' check destination_was_mounted and um-mount destination if required '''
            if not destination_was_mounted:
                unmount_destination = unMountDestination(destination)
        except subprocess.CalledProcessError as ex:
            print(destination, 'mounted before loop start: ', destination_was_mounted)
            handleCalledProcessError(ex)
        except NoCheckFile as ex:
            handleNoCheckFile(ex)
        else:
            print(destination, 'mounted before loop start: ', destination_was_mounted)
            logExecute(mount_destination)
            logExecute(check_destination)
        finally:
            print('should always see me')
            logExecute(unmount_destination)
            # return to say True or False

    # this should be where email reports etc. go

if __name__ == '__main__':
    main()

backup.ini文件的相关部分是：

[general]

[1]
DESTINATION = /mnt/backup2
BACKUP_DIR = BACKUP2
CHECKFILE = .checkfile

[2]
DESTINATION = /mnt/backup1
BACKUP_DIR = BACKUP1
CHECKFILE = .checkfile

输出如下所示 - 我在[1]和[2]中指定的挂载点附加了2个备份磁盘，故意没有创建[1]的检查文件进行测试。

> umount /mnt/backup1
umount: /mnt/backup1: not mounted
> umount /mnt/backup2 
umount: /mnt/backup2: not mounted
> mugsyback.py 
Exception: no checkfile found
should always see me
Info: None
/mnt/backup1 mounted before loop start:  False
Info: 0
Info: True
should always see me
Info: 0
> mount
...
/dev/sdc1 on /mnt/backup2 type ext3 (rw)

Answer 1

您在try块中有卸载代码。最后，你只是记录。

Python：在try / except / else块中引发异常，处理顺序问题

1 个答案: