loggertest.py

import logging

logger = logging.getLogger('xxx')
logging.lastResort.setLevel(logging.DEBUG)  # <<<<<< コレ！

for lvl in (logging.DEBUG, logging.INFO,
            logging.WARNING, logging.ERROR, logging.CRITICAL):
    logger.setLevel(lvl)

    print(logger.level)
    logger.debug('debug')
    logger.info('info')
    logger.warning('warning')
    logger.error('error')
    logger.critical('critical')
    print()