time模块

逝去的秒数

逝去的秒数表示从某个时间（Python中是“Thu Jan 1 07:00:00 1970”）开始到现在所经过的秒数。

使用 time.time() 函数可以获得逝去的秒数：

>>time.time()
1388330058.8643

time.time()返回一个浮点数，可用于计算，比较，存储时间时间。

输出可读性强的时间字符串

要输出像“Thu Jan 1 07:00:00 1970”这种可读性强的时间字符串，我们可以使用 time.ctime() 函数，默认返回当前的时间：

>>> time.ctime()
'Sun Dec 29 23:17:44 2013'

也可以传入一个逝去的秒数，返回对应的时间字符串：

>>> time.ctime(0)
'Thu Jan  1 07:00:00 1970'

获取时间的各个部分信息

我们经常要分别获取一个时间的年、月、日、时、分、秒等信息，time模块定义了一个 struct_time 类型，用来存储时间的各个部分信息。该类型实现了元组协议，所以可以当作元组使用。

struct_time 的结构如下：

Index	Attribute	Values
0	`tm_year`	(for example, 1993)
1	`tm_mon`	range [1, 12]
2	`tm_mday`	range [1, 31]
3	`tm_hour`	range [0, 23]
4	`tm_min`	range [0, 59]
5	`tm_sec`	range [0, 61];
6	`tm_wday`	range [0, 6], Monday is 0
7	`tm_yday`	range [1, 366]
8	`tm_isdst`	0, 1 or -1; see below

有几个函数都可以返回struct_time, gmtime() 返回当前的UTC时间，localtime() 返回当前时间域的当前时间：

>>> time.gmtime()
time.struct_time(tm_year=2013, tm_mon=12, tm_mday=29, tm_hour=15, tm_min=35, tm_sec=57, tm_wday=6, tm_yday=363, tm_isdst=0)
>>> time.localtime()
time.struct_time(tm_year=2013, tm_mon=12, tm_mday=29, tm_hour=23, tm_min=36, tm_sec=6, tm_wday=6, tm_yday=363, tm_isdst=0)

gmtime() 和 localtime() 也接受一个逝去的秒数作为参数，并转换成struct_time：

>>> time.localtime(0)
time.struct_time(tm_year=1970, tm_mon=1, tm_mday=1, tm_hour=7, tm_min=0, tm_sec=0, tm_wday=3, tm_yday=1, tm_isdst=0)

mktime() 接收 struct_time 参数并将其转化为逝去的秒数：

>>> time.mktime(time.localtime())
1388331386.0

解析和格式化时间

如何将类似”Sun Dec 29 23:17:44 2013“的字符串解析成 struct_time？

time模块提供了两个函数来处理这方面的工作。函数 strptime() 用于将时间字符串解析成 struct_time，函数 strftime() 则将 struct_time 格式化成可读性强的时间字符串

import timenow = time.ctime()
print now
parsed = time.strptime(now)
print parsed
print time.strftime("%a %b %d %H:%M:%S %Y", parsed)# output =>
# Sun Mar  9 13:01:19 2008
# (2008, 3, 9, 13, 1, 19, 6, 69, -1)
# Sun Mar 09 13:01:19 2008

这两个函数都依赖特定的格式说明信息，默认的格式说明为”%a %b %d %H:%M:%S %Y“。完整的格式列表可以在https://docs.python.org/2/library/time.html#time.strftime找到。

Directive	Meaning	Notes
`%a`	Locale’s abbreviated weekday name.
`%A`	Locale’s full weekday name.
`%b`	Locale’s abbreviated month name.
`%B`	Locale’s full month name.
`%c`	Locale’s appropriate date and time representation.
`%d`	Day of the month as a decimal number [01,31].
`%H`	Hour (24-hour clock) as a decimal number [00,23].
`%I`	Hour (12-hour clock) as a decimal number [01,12].
`%j`	Day of the year as a decimal number [001,366].
`%m`	Month as a decimal number [01,12].
`%M`	Minute as a decimal number [00,59].
`%p`	Locale’s equivalent of either AM or PM.	(1)
`%S`	Second as a decimal number [00,61].	(2)
`%U`	Week number of the year (Sunday as the first day of the week) as a decimal number [00,53]. All days in a new year preceding the first Sunday are considered to be in week 0.	(3)
`%w`	Weekday as a decimal number [0(Sunday),6].
`%W`	Week number of the year (Monday as the first day of the week) as a decimal number [00,53]. All days in a new year preceding the first Monday are considered to be in week 0.	(3)
`%x`	Locale’s appropriate date representation.
`%X`	Locale’s appropriate time representation.
`%y`	Year without century as a decimal number [00,99].
`%Y`	Year with century as a decimal number.
`%Z`	Time zone name (no characters if no time zone exists).
`%%`	A literal `'%'` character.