loglevelは正の整数でないといけない

getoptで-vの数だけloglevel -= 10してたらハマった。

>>> import logging
>>> logging.getLogger('root')
<logging.Logger instance at 0xb7d12cac>
>>> log = _
>>> log
<logging.Logger instance at 0xb7d12cac>
>>> log.debug('foo')
>>> log.setLevel(10)
>>> log.debug('foo')
No handlers could be found for logger "root"
>>> import sys
>>> logging.basicConfig(stream=sys.stderr)
>>> log.debug('foo')
DEBUG:root:foo
>>> log.setLevel(0)
>>> log.debug('foo')
>>> log.setLevel(1) 
>>> log.debug('foo')
DEBUG:root:foo