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]; see (2) in strftime() description |
| 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 time
now = 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. |