#datetime
import datetime
#当前日期
now = datetime.datetime.now()
print(now.strftime('%Y-%m-%d %H:%M:%S'))
print(now.strftime('%Y-%m-%d'))
#string convert to datetime
time_str = '2013-07-29 01:05:00'
str_convert_2_time = datetime.datetime.strptime(time_str, '%Y-%m-%d %H:%M:%S')
print(str_convert_2_time)
#比较两个日期相差多少天
time_strA = '2013-07-29 01:05:00'
time_strB ='2013-08-29 01:05:00' 
day = datetime.datetime.strptime(time_strA, '%Y-%m-%d %H:%M:%S')
day2 = datetime.datetime.strptime(time_strB, '%Y-%m-%d %H:%M:%S')
sub_day = day2 - day
print('{0}和{1}相差{2}天'.format(time_strA, time_strB, str(sub_day.days)))
#今后的n天的日期
n_days = 4
now = datetime.datetime.now()
my_date = datetime.timedelta(days=n_days) 
n_day = now + my_date
print('从今天起的{0}天的日期是：'.format(n_days))
print(n_day.strftime('%Y-%m-%d %H:%M:%S'))

Python 3.3.2 (v3.3.2:d047928ae3f6, May 16 2013, 00:03:43) [MSC v.1600 32 bit (Intel)] on win32
Type "copyright", "credits" or "license()" for more information.
>>> ================================ RESTART ================================
>>> 
2013-07-29 01:48:16
2013-07-29
2013-07-29 01:05:00
2013-07-29 01:05:00和2013-08-29 01:05:00相差31天
从今天起的4天的日期是：
2013-08-02 01:48:16
>>>