python日期函数<转>

# -*- coding: utf-8 -*-

from  datetime import datetime
import time

# 取当前时间，返回string类型
now_str = time.strftime("%Y-%m-%d %H:%M:%S") 
print (type(now_str))    
print now_str
print '---'

# 取当前时间,返回datetime类型
print (type(datetime.now()))    
print datetime.now()
print '---'

# string -> datetime
time_type = datetime.strptime(now_str, "%Y-%m-%d %H:%M:%S") 
print type(time_type)
print time_type
print '---'

# datetime -> string
str_type = datetime.strftime(time_type, "%Y-%m-%d %H:%M:%S") 
print type(str_type)
print str_type

#计算时间间隔
starttime = datetime.now()
endtime = datetime.now()
print (endtime - starttime).seconds

# 构造datetime对象
new_dt = datetime(2005, 2, 16)
print type(new_dt)
print new_dt

# 日期计算,这里需要datetime，而不是datetime.datetime
yesterday_date = datetime.datetime.now() - datetime.timedelta(days=1)  
yesterday_str = datetime.datetime.strftime(yesterday_date, "%Y%m%d")