python中or语句的妙用，一行代替if/elif/else多行代码

import os

args = {'search_engine':'baidu'}
if args['search_engine']:
	search_engine = args['search_engine']
elif os.getenv('HOWDOI_SEARCH_ENGINE'):
	search_engine = os.getenv('HOWDOI_SEARCH_ENGINE')
else:
	search_engine = 'bing'

print(search_engine)

import os

search_engine = args['search_engine'] or os.getenv('HOWDOI_SEARCH_ENGINE') or 'bing'

print(search_engine)

机制：第一个不存在则判断第二个是否存在，若第二个不存在则判读第三个是否存在