In [27]: from datetime import datetime

In [28]: a=datetime.now()

In [29]: b=datetime.now()

In [32]: a
Out[32]: datetime.datetime(2015, 4, 7, 4, 30, 3, 628556)

In [33]: b
Out[33]: datetime.datetime(2015, 4, 7, 4, 34, 41, 907292)

In [34]: str(a)                   字符串的转换，用户储存到文本或者数据库
Out[34]: '2015-04-07 04:30:03.628556'

In [35]:datetime.strptime(str(a),"%Y-%m-%d %H:%M:%S.%f")
Out[35]:datetime.datetime(2015, 4, 7, 4, 30, 3, 628556)

In [36]: (b-a)
Out[36]: datetime.timedelta(0, 278, 278736)

In [37]: (b-a).seconds              时间差的计算，单位为秒
Out[37]: 278

>>> import datetime
>>> d1 = datetime.datetime(2005, 2, 16)
>>> d2 = datetime.datetime(2004, 12, 31)
>>> (d1 - d2).days
47

import datetime
starttime = datetime.datetime.now()
#long running
endtime = datetime.datetime.now()
print (endtime - starttime).seconds

>>> d1 = datetime.datetime.now()
>>> d3 = d1 + datetime.timedelta(hours=10)
>>> d3.ctime()