python时间计算及表达

写脚本的时候会用到到但又不算太频繁,导致经常要去翻google....干脆都记下来

先是python的

>>> import time
>>> print time.localtime()
(2013, 8, 9, 14, 17, 30, 4, 221, 0)
>>> print type(time.localtime())
<type 'time.struct_time'>
>>> curTime = time.strftime('%Y-%m-%d %H:%M:%S',time.localtime())
>>> print curTime
2013-08-09 14:17:11
>>> print type(curTime)
<type 'str'>
>>> time.time()
1376029404.869349
>>> print type(time.time())
<type 'float'>

datetime
http://blog.csdn.net/jgood/article/details/5457284

>>> import datetime
>>> datetime.datetime.now()
datetime.datetime(2013, 8, 9, 14, 26, 47, 350944)
>>> loli = datetime.datetime.now()
>>> print loli
2013-08-09 14:26:57.998630
>>> print type(loli)
<type 'datetime.datetime'>
>>> datetime.datetime.now()-loli
datetime.timedelta(0, 40, 878765)
>>> lolita = datetime.datetime.now()-loli
>>> print lolita
0:00:48.414427
>>> print lolita.days
0
>>> print lolita.seconds
48
>>> date_up = datetime.timedelta(days=3)
>>> print type(date_up)
<type 'datetime.timedelta'>
>>> print date_up.days
3
>>> lolicon = loli - date_up
>>> print lolicon
2013-08-06 14:26:57.998630
>>> print (lolicon>loli)
False

顺便https://blog.lzhaohao.info/archive/performance-problem-with-strptime/
简单来说就通过正则把时间什么的纷纷作为int传给datetime处理，这样比strptime直接处理字符串要快
而且这样做最大的好处就是....pthon2.4里datetime没有strptime这个模块>_<

#!/usr/bin/env python
import datetime
import os
import re
import timeit, cProfile

def strptime():
    with open('time.txt', 'r') as f:
        for line in f:
            line = line.rstrip(os.linesep)
            dt = datetime.datetime.strptime(line, "%Y-%m-%d %H:%M:%S")


def reg():
    rep = re.compile(r'(\d{4})-(\d{2})-(\d{2})\s(\d{2}):(\d{2}):(\d{2})')
    with open('time.txt', 'r') as f:
        for line in f:
            line = line.rstrip(os.linesep)
            m = rep.match(line)
            dt = datetime.datetime(int(m.group(1)),
             int(m.group(2)),
             int(m.group(3)),
             int(m.group(4)),
             int(m.group(5)),
             int(m.group(6))
             )

if __name__ == '__main__':

    t1 = timeit.Timer("reg()","from __main__ import reg")
    t2 = timeit.Timer("strptime()", "from __main__ import strptime")

    cProfile.run("t1.timeit(3);print")
    print""
    cProfile.run("t2.timeit(3);print")

一些计算例子

#获取昨天的写法

one_difference_day = datetime.timedelta(1,0,0)
today = datetime.datetime.now()
yesterday = today - one_difference_day

#只要日期(这个的返回依旧是datetime类)
yesterday.date()

#分别获取年月日（注意yesterday有hour、minute、second等属性,yesterday.date()没有这些属性）
print '%s-%s-%s' % (yesterday.year,yesterday.month,yesterday.day)

#上面那个写法有明显缺点,就是小于10的日/月前面没0,改良写法
print '%s' % yesterday.date().isoformat()

上面写法都是用datetime.date()把datetime类里的小时，分秒毫秒属性去除，还有另外一个方法
可以直接用datetime.replace([year[, month[, day[, hour[, minute[, second[, microsecond[, tzinfo]]]]]]]])把小时，分秒毫秒属性设置成0，然后再计算。
更多用法参考http://blog.csdn.net/jgood/article/details/5457284


不同格式的字符串时间传换
str 转 datetime 用 datetime.datetime.strptime(str,'格式')
datetime 转str 用 datetime的方法 strftime('格式')

一个例子：一个字符串格式是30/Dec/2013,我们要把这个时间转换为2013-12-30
可以用如下转换方式
time_str = '30/Dec/2013'
log_date = datetime.datetime.strptime(time_str,'%d/%b/%Y').strftime('%Y-%m-%d')
上面的加上try还可以用于判断字符串是否为所指定的时间格式，中途转化为datetime以后还可以计算完毕再转换str

昨天的新写法,其实和上面差不多

today = datetime.datetime.now().date()
difference_day = datetime.timedelta(days=1)
yesterday = (today - difference_day).strftime('%Y-%m-%d')

上个月的计算方法，以及上个月天数的计算方法，比较常用

year = datetime.datetime.now().year
last_moth = datetime.datetime.now().month - 1
if last_moth == 0:
    last_moth = 12
    year -= 1
day_long = (datetime.datetime(datetime.datetime.now().year, datetime.datetime.now().month, 01) -
                datetime.datetime(year, last_moth, 01)).days

unix时间转datetime
datetime.datetime.fromtimestamp(1396256636)
只算日期
datetime.date.fromtimestamp(1396256636)
混一起说明
print(datetime.datetime.fromtimestamp(int("1284101485")).strftime('%Y-%m-%d %H:%M:%S'))

datetime转unix时间比较麻烦，因为datetime本身不支持直接转unix时间，只能把datetime转成timetuple，再用time.mktime转换成unix时间
today = datetime.datetime.strptime('2014-09-27', '%Y-%m-%d')
int_today = time.mktime(compute_day.date().timetuple())

一个很好的说明图，转自
http://blog.sina.com.cn/s/blog_b09d460201018o0v.html