详解Python编程中time模块的使用
一、简介
time模块提供各种操作时间的函数
说明：一般有两种表示时间的方式:
第一种是时间戳的方式(相对于1970.1.1 00:00:00以秒计算的偏移量),时间戳是惟一的
第二种以数组的形式表示即(struct_time),共有九个元素，分别表示，同一个时间戳的struct_time会因为时区不同而不同
- year (four digits, e.g. 1998)
- month (1-12)
- day (1-31)
- hours (0-23)
- minutes (0-59)
- seconds (0-59)
- weekday (0-6, Monday is 0)
- Julian day (day in the year, 1-366)
- DST (Daylight Savings Time) flag (-1, 0 or 1) 是否是夏令时
- If the DST flag is 0, the time is given in the regular time zone;
- if it is 1, the time is given in the DST time zone;
- if it is -1, mktime() should guess based on the date and time.
夏令时介绍：http://baike.baidu.com/view/100246.htm
UTC介绍：http://wenda.tianya.cn/wenda/thread?tid=283921a9da7c5aef&clk=wttpcts
二、函数介绍
1.asctime()
asctime([tuple]) -> string
将一个struct_time(默认为当时时间)，转换成字符串
Convert a time tuple to a string, e.g. ‘Sat Jun 06 16:26:11 1998'.
When the time tuple is not present, current time as returned by localtime() is used.
2.clock()
clock() -> floating point number
该函数有两个功能，
在第一次调用的时候，返回的是程序运行的实际时间；
以第二次之后的调用，返回的是自第一次调用后,到这次调用的时间间隔
注：
在Xinux上使用 time.time() 而在windows中使用time.clock()可以得到更高的精度.
Xinux和Win在实现系统时钟的不同。time.clock()是调用的系统时钟实现，而两个平台又有所不同。
主要问题在于Xinux时钟切换策略:jiffy的实现，因为内核时钟的切换不是连续的而是间隔一段时间（一般而言在1ms~10ms之间）之后才变化， 所以如果是在Xinux中的两次耗时较短的调用，通过time.clock()得到的结果是一样的。
3.sleep(…)
sleep(seconds)
线程推迟指定的时间运行，经过测试，单位为秒
示例：
import time
if __name__ == '__main__':
time.sleep(3)
print "clock1: %s" % time.clock()
# print "local time: %s" % time.localtime()
print str(time.strftime('%Y-%m-%d %H:%M:%S', time.localtime()))
time.sleep(3)
print "clock2: %s" % time.clock()
# print "local time: %s" % time.localtime()
print str(time.strftime('%Y-%m-%d %H:%M:%S', time.localtime()))
time.sleep(3)
print "clock3: %s" % time.clock()
# print "local time: %s" % time.localtime()
print str(time.strftime('%Y-%m-%d %H:%M:%S', time.localtime()))
结果
clock1: 0.020678 2015-08-09 00:18:31 clock2: 0.020891 2015-08-09 00:18:34 clock3: 0.021068 2015-08-09 00:18:37
4.ctime(…)
ctime(seconds) -> string
将一个时间戳(默认为当前时间)转换成一个时间字符串
例如：
time.ctime()
输出为：
'Sat Mar 28 22:24:24 2009′
5.gmtime(…)
gmtime([seconds]) -> (tm_year, tm_mon, tm_day, tm_hour, tm_min,tm_sec, tm_wday, tm_yday, tm_isdst)
将一个时间戳转换成一个UTC时区(0时区)的struct_time，如果seconds参数未输入，则以当前时间为转换标准
6.localtime(…)
localtime([seconds]) -> (tm_year,tm_mon,tm_day,tm_hour,tm_min,tm_sec,tm_wday,tm_yday,tm_isdst)
将一个时间戳转换成一个当前时区的struct_time，如果seconds参数未输入，则以当前时间为转换标准
7.mktime(…)
mktime(tuple) -> floating point number
将一个以struct_time转换为时间戳
8.strftime(…)
strftime(format[, tuple]) -> string
将指定的struct_time(默认为当前时间)，根据指定的格式化字符串输出
python中时间日期格式化符号：
- %y 两位数的年份表示（00-99）
- %Y 四位数的年份表示（000-9999）
- %m 月份（01-12）
- %d 月内中的一天（0-31）
- %H 24小时制小时数（0-23）
- %I 12小时制小时数（01-12）
- %M 分钟数（00=59）
- %S 秒（00-59）
- %a 本地简化星期名称
- %A 本地完整星期名称
- %b 本地简化的月份名称
- %B 本地完整的月份名称
- %c 本地相应的日期表示和时间表示
- %j 年内的一天（001-366）
- %p 本地A.M.或P.M.的等价符
- %U 一年中的星期数（00-53）星期天为星期的开始
- %w 星期（0-6），星期天为星期的开始
- %W 一年中的星期数（00-53）星期一为星期的开始
- %x 本地相应的日期表示
- %X 本地相应的时间表示
- %Z 当前时区的名称
- %% %号本身
print str(time.strftime('%Y-%m-%d %H:%M:%S', time.localtime()))
2015-08-09 00:18:37
9.strptime(…)
strptime(string, format) -> struct_time
将时间字符串根据指定的格式化符转换成数组形式的时间
例如：
2009-03-20 11:45:39 对应的格式化字符串为：%Y-%m-%d %H:%M:%S
Sat Mar 28 22:24:24 2009 对应的格式化字符串为：%a %b %d %H:%M:%S %Y
10.time(…)
time() -> floating point number
返回当前时间的时间戳（1970纪元后经过的浮点秒数）
三、常用命令
1.python获取当前时间
time.time() 获取当前时间戳
time.localtime() 当前时间的struct_time形式
time.ctime() 当前时间的字符串形式
print time.time() print time.localtime() print time.ctime()
结果为：
1439051479.08 time.struct_time(tm_year=2015, tm_mon=8, tm_mday=9, tm_hour=0, tm_min=31, tm_sec=19, tm_wday=6, tm_yday=221, tm_isdst=0) Sun Aug 9 00:31:19 2015
2.python格式化字符串
格式化成2009-03-20 11:45:39形式
time.strftime(“%Y-%m-%d %H:%M:%S”, time.localtime())
格式化成Sat Mar 28 22:24:24 2009形式
time.strftime(“%a %b %d %H:%M:%S %Y”, time.localtime())
3.将格式字符串转换为时间戳
a = “Sat Mar 28 22:24:24 2009″
b = time.mktime(time.strptime(a,”%a %b %d %H:%M:%S %Y”))
ps:
了解这一块主要是想用time来计算我程序中关键既不的运行时间，所以更多整理这部分内容。至于时间的转化等，后续用得着的时候再来整理。
四、使用time模块计算代码执行效率的精度测试
#python中使用time模块计算代码执行效率 #测试用time.time()和time.clock()使用精度 import sys import time import timeit default_timer = None if sys.platform == "win32": # On Windows, the best timer is time.clock() default_timer = time.clock else: # On most other platforms the best timer is time.time() default_timer = time.time print default_timer timeIn= time.clock() for i in range(100): n=i timeUse = time.clock()-timeIn print timeUse timeIn = time.time() for i in range(100): n=i timeUse = time.time()-timeIn print timeUse timeIn = timeit.default_timer() for i in range(100): n=i timeUse = timeit.default_timer()-timeIn print timeUse #该段代码在windows下结果如下 >>> 4.07873067161e-005 0.0 3.5758734839e-005 #因为time.clock() 返回的是处理器时间，而因为 Unix 中 jiffy 的缘故，所以精度不会太高。 #因此，在Windows 系统中，建议使用 time.clock()，在Unix 系统中，建议使用 time.time()， #而使用timeit代替 time，就可以实现跨平台的精度性，使用timeit.default_timer()函数来获取时间
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