python如何计算时间差

from datetime import datetime

a=datetime.now()

b=datetime.now()

>>>a

>>>datetime.datetime(2015, 4, 7, 4, 30, 3, 628556)

>>>b

>>>datetime.datetime(2015, 4, 7, 4, 34, 41, 907292)

>>>str(a) #字符串的转换，用户储存到文本或者数据库

'2015-04-07 04:30:03.628556'

>>>datetime.strptime(str(a),"%Y-%m-%d %H:%M:%S.%f")

datetime.datetime(2015, 4, 7, 4, 30, 3, 628556)

>>> (b-a)

Out: datetime.timedelta(0, 278, 278736)

>>>(b-a).seconds #时间差的计算，单位为秒

278

>>> import datetime

>>> d1 = datetime.datetime(2005, 2, 16)

>>> d2 = datetime.datetime(2004, 12, 31)

>>> (d1 - d2).days47

>>>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()