python日期函数<转>

 1 # -*- coding: utf-8 -*-
 2 
 3 from  datetime import datetime
 4 import time
 5 
 6 # 取当前时间，返回string类型
 7 now_str = time.strftime("%Y-%m-%d %H:%M:%S") 
 8 print (type(now_str))    
 9 print now_str
10 print '---'
11 
12 # 取当前时间,返回datetime类型
13 print (type(datetime.now()))    
14 print datetime.now()
15 print '---'
16 
17 # string -> datetime
18 time_type = datetime.strptime(now_str, "%Y-%m-%d %H:%M:%S") 
19 print type(time_type)
20 print time_type
21 print '---'
22 
23 # datetime -> string
24 str_type = datetime.strftime(time_type, "%Y-%m-%d %H:%M:%S") 
25 print type(str_type)
26 print str_type
27 
28 #计算时间间隔
29 starttime = datetime.now()
30 endtime = datetime.now()
31 print (endtime - starttime).seconds
32 
33 # 构造datetime对象
34 new_dt = datetime(2005, 2, 16)
35 print type(new_dt)
36 print new_dt
37 
38 # 日期计算,这里需要datetime，而不是datetime.datetime
39 yesterday_date = datetime.datetime.now() - datetime.timedelta(days=1)  
40 yesterday_str = datetime.datetime.strftime(yesterday_date, "%Y%m%d")