转载:http://www.cnblogs.com/rollenholt/archive/2012/04/10/2441542.html
1.datetime => string
now = datetime.datetime.now()
now.strftime('%Y-%m-%d %H:%M:%S')
输出2012-03-05 16:26:23.870105
strftime是datetime类的实例方法。
2.string => datetime
t_str = '2012-03-05 16:26:23'
d = datetime.datetime.strptime(t_str, '%Y-%m-%d %H:%M:%S')