【整理】Python中字符串与时间的转换与计算

一、string time datetime之间的相互转换

1、string->time

>>> time.strptime('2012-08-04', '%Y-%m-%d')
time.struct_time(tm_year=2012, tm_mon=8, tm_mday=4, tm_hour=0, tm_min=0, tm_sec=0, tm_wday=5, tm_yday=217, tm_isdst=-1)

2、time->string

>>> import time

#方法1
>>> time.strftime('%Y-%m-%d', time.localtime()) #'2012-08-04'

#方法2
>>> time.strftime('%Y-%m-%d', time.localtime(time.time())) #'2012-08-04'

其中strftime(应该是string format time的意思)用来格式化时间，第一个参数为格式化字符串，第二个参数为一个结构体struct，而time.time()函数则是获取机器时间

3、string -> datetime

#方法1

按string->time->datetime进行转化

>>> import datetime
>>> datetime.datetime(*time.strptime('2012-08-04', '%Y-%m-%d')[:3])    #datetime.datetime(2012, 8, 4, 0, 0)

#方法2

>>> import datetime

>>> datetime.datetime.strptime('2012-08-04', '%Y-%m-%d') #datetime.datetime(2012, 8, 4, 0, 0)

4、datetime -> string 

>>> import datetime

>>> now = time.localtime()

>>> dt = datetime.datetime(*now[:3])

#按指定的格式返回字符串

>>> dt.strftime(format='%Y-%m-%d')  #'2012-08-04'

#默认格式返回字符串

>>> dt.ctime() #'Sat Aug  4 00:00:00 2012'

5、time -> datetime

>>> import datetime
>>> now = time.localtime()

>>> datetime.datetime(*now[:3])    #datetime.datetime(2012, 8, 4, 0, 0)

6、datetime -> time

>>> dt.timetuple()
输出：time.struct_time(tm_year=2012, tm_mon=8, tm_mday=4, tm_hour=0, tm_min=0, tm_sec=0, tm_wday=5, tm_yday=217, tm_isdst=-1)

 

二、datetime的计算

datetime的加减会涉及timedelta

1、时间相减

>>> dt1 = datetime.datetime(2012, 8, 4, 20, 33, 34)
>>> dt2 = datetime.datetime(2012, 7, 5, 14, 22, 32)
>>> dt1-dt2 #datetime.timedelta(30, 22262)

>>> (dt1-dt2).days   #30

2、一段时间之后或之前

>>> dt1+datetime.timedelta(days=10) #datetime.datetime(2012, 8, 14, 20, 33, 34)

>>> dt1-datetime.timedelta(days=10)  #datetime.datetime(2012, 7, 25, 20, 33, 34)

>>> dt4 = datetime.date(2012, 8, 14)
>>> dt5 = datetime.date(2012, 7, 22)
>>> dt4-dt5 #datetime.timedelta(23)