import logging
import sys

LEVELS = { 'debug': logging.DEBUG,
            'info': logging.INFO,
            'warning': logging.WARNING,
            'error': logging.ERROR,
            'critical': logging.CRITICAL
}

if len(sys.argv) > 1:
    level_name = sys.argv[1]
    level = LEVELS.get(level_name, logging.NOTSET)
    logging.basicConfig(level=level)

logging.debug('This is a debug message')
logging.info('This is an info message')
logging.warning('This is a warning message')
logging.error('This is an error message')
logging.critical('This is a critical error message')