==time 模块==
``time`` 模块提供了一些处理日期和一天内时间的函数. 它是建立在 C 运行时库的简单封装.
给定的日期和时间可以被表示为浮点型(从参考时间, 通常是 1970.1.1 到现在经过的秒数.
即 Unix 格式), 或者一个表示时间的 struct (类元组).
=== 获得当前时间===
[Example 1-79 #eg-1-79] 展示了如何使用 ``time`` 模块获取当前时间.
====Example 1-79. 使用 time 模块获取当前时间====[eg-1-79]
```
File: time-example-1.py
import time
now = time.time()
print now, "seconds since", time.gmtime(0)[:6]
print
print "or in other words:"
print "- local time:", time.localtime(now)
print "- utc:", time.gmtime(now)
*B*937758359.77 seconds since (1970, 1, 1, 0, 0, 0)
or in other words:
- local time: (1999, 9, 19, 18, 25, 59, 6, 262, 1)
- utc: (1999, 9, 19, 16, 25, 59, 6, 262, 0)*b*
```
``localtime`` 和 ``gmtime`` 返回的类元组包括年, 月, 日, 时, 分, 秒, 星期, 一年的第几天, 日光标志.
其中年是一个四位数(在有千年虫问题的平台上另有规定, 但还是四位数), 星期从星期一(数字 0 代表)开始,
1月1日是一年的第一天.
=== 将时间值转换为字符串===
你可以使用标准的格式化字符串把时间对象转换为字符串, 不过 ``time`` 模块已经提供了许多标准转换函数,
如 [Example 1-80 #eg-1-80] 所示.
====Example 1-80. 使用 time 模块格式化时间输出====[eg-1-80]
```
File: time-example-2.py
import time
now = time.localtime(time.time())
print time.asctime(now)
print time.strftime("%y/%m/%d %H:%M", now)
print time.strftime("%a %b %d", now)
print time.strftime("%c", now)
print time.strftime("%I %p", now)
print time.strftime("%Y-%m-%d %H:%M:%S %Z", now)
# do it by hand...
year, month, day, hour, minute, second, weekday, yearday, daylight = now
print "%04d-%02d-%02d" % (year, month, day)
print "%02d:%02d:%02d" % (hour, minute, second)
print ("MON", "TUE", "WED", "THU", "FRI", "SAT", "SUN")[weekday], yearday
*B*Sun Oct 10 21:39:24 1999
99/10/10 21:39
Sun Oct 10
Sun Oct 10 21:39:24 1999
09 PM
1999-10-10 21:39:24 CEST
1999-10-10
21:39:24
SUN 283*b*
```
===将字符串转换为时间对象===
在一些平台上, ``time`` 模块包含了 ``strptime`` 函数, 它的作用与 ``strftime`` 相反.
给定一个字符串和模式, 它返回相应的时间对象, 如 [Example 1-81 #eg-1-81] 所示.
====Example 1-81. 使用 time.strptime 函数解析时间====[eg-1-81]
```
File: time-example-6.py
import time
# make sure we have a strptime function!
# 确认有函数 strptime
try:
strptime = time.strptime
except AttributeError:
from strptime import strptime
print strptime("31 Nov 00", "%d %b %y")
print strptime("1 Jan 70 1:30pm", "%d %b %y %I:%M%p")
```
只有在系统的 C 库提供了相应的函数的时候, ``time.strptime`` 函数才可以使用.
对于没有提供标准实现的平台, [Example 1-82 #eg-1-82] 提供了一个不完全的实现.
====Example 1-82. strptime 实现====[eg-1-82]
```
File: strptime.py
import re
import string
MONTHS = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug",
"Sep", "Oct", "Nov", "Dec"]
SPEC = {
# map formatting code to a regular expression fragment
"%a": "(?P<weekday>[a-z]+)",
"%A": "(?P<weekday>[a-z]+)",
"%b": "(?P<month>[a-z]+)",
"%B": "(?P<month>[a-z]+)",
"%C": "(?P<century>\d\d?)",
"%d": "(?P<day>\d\d?)",
"%D": "(?P<month>\d\d?)/(?P<day>\d\d?)/(?P<year>\d\d)",
"%e": "(?P<day>\d\d?)",
"%h": "(?P<month>[a-z]+)",
"%H": "(?P<hour>\d\d?)",
"%I": "(?P<hour12>\d\d?)",
"%j": "(?P<yearday>\d\d?\d?)",
"%m": "(?P<month>\d\d?)",
"%M": "(?P<minute>\d\d?)",
"%p": "(?P<ampm12>am|pm)",
"%R": "(?P<hour>\d\d?):(?P<minute>\d\d?)",
"%S": "(?P<second>\d\d?)",
"%T": "(?P<hour>\d\d?):(?P<minute>\d\d?):(?P<second>\d\d?)",
"%U": "(?P<week>\d\d)",
"%w": "(?P<weekday>\d)",
"%W": "(?P<weekday>\d\d)",
"%y": "(?P<year>\d\d)",
"%Y": "(?P<year>\d\d\d\d)",
"%%": "%"
}
class TimeParser:
def _ _init_ _(self, format):
# convert strptime format string to regular expression
format = string.join(re.split("(?:\s|%t|%n)+", format))
pattern = []
try:
for spec in re.findall("%\w|%%|.", format):
if spec[0] == "%":
spec = SPEC[spec]
pattern.append(spec)
except KeyError:
raise ValueError, "unknown specificer: %s" % spec
self.pattern = re.compile("(?i)" + string.join(pattern, ""))
def match(self, daytime):
# match time string
match = self.pattern.match(daytime)
if not match:
raise ValueError, "format mismatch"
get = match.groupdict().get
tm = [0] * 9
# extract date elements
y = get("year")
if y:
y = int(y)
if y < 68:
y = 2000 + y
elif y < 100:
y = 1900 + y
tm[0] = y
m = get("month")
if m:
if m in MONTHS:
m = MONTHS.index(m) + 1
tm[1] = int(m)
d = get("day")
if d: tm[2] = int(d)
# extract time elements
h = get("hour")
if h:
tm[3] = int(h)
else:
h = get("hour12")
if h:
h = int(h)
if string.lower(get("ampm12", "")) == "pm":
h = h + 12
tm[3] = h
m = get("minute")
if m: tm[4] = int(m)
s = get("second")
if s: tm[5] = int(s)
# ignore weekday/yearday for now
return tuple(tm)
def strptime(string, format="%a %b %d %H:%M:%S %Y"):
return TimeParser(format).match(string)
if _ _name_ _ == "_ _main_ _":
# try it out
import time
print strptime("2000-12-20 01:02:03", "%Y-%m-%d %H:%M:%S")
print strptime(time.ctime(time.time()))
*B*(2000, 12, 20, 1, 2, 3, 0, 0, 0)
(2000, 11, 15, 12, 30, 45, 0, 0, 0)*b*
```
=== 转换时间值===
将时间元组转换回时间值非常简单, 至少我们谈论的当地时间 (local time) 如此.
只要把时间元组传递给 ``mktime`` 函数, 如 [Example 1-83 #eg-1-83] 所示.
====Example 1-83. 使用 time 模块将本地时间元组转换为时间值(整数)====[eg-1-83]
```
File: time-example-3.py
import time
t0 = time.time()
tm = time.localtime(t0)
print tm
print t0
print time.mktime(tm)
*B*(1999, 9, 9, 0, 11, 8, 3, 252, 1)
936828668.16
936828668.0*b*
```
但是, 1.5.2 版本的标准库没有提供能将 UTC 时间
(Universal Time, Coordinated: 特林威治标准时间)转换为时间值的函数
( Python 和对应底层 C 库都没有提供). [Example 1-84 #eg-1-84] 提供了该函数的一个
Python 实现, 称为 ``timegm`` .
====Example 1-84. 将 UTC 时间元组转换为时间值(整数)====[eg-1-84]
```
File: time-example-4.py
import time
def _d(y, m, d, days=(0,31,59,90,120,151,181,212,243,273,304,334,365)):
# map a date to the number of days from a reference point
return (((y - 1901)*1461)/4 + days[m-1] + d +
((m > 2 and not y % 4 and (y % 100 or not y % 400)) and 1))
def timegm(tm, epoch=_d(1970,1,1)):
year, month, day, h, m, s = tm[:6]
assert year >= 1970
assert 1 <= month <= 12
return (_d(year, month, day) - epoch)*86400 + h*3600 + m*60 + s
t0 = time.time()
tm = time.gmtime(t0)
print tm
print t0
print timegm(tm)
*B*(1999, 9, 8, 22, 12, 12, 2, 251, 0)
936828732.48
936828732*b*
```
从 1.6 版本开始, ``calendar`` 模块提供了一个类似的函数 ``calendar.timegm`` .
=== Timing 相关===
``time`` 模块可以计算 Python 程序的执行时间, 如 [Example 1-85 #eg-1-85] 所示.
你可以测量 "wall time" (real world time), 或是"进程时间" (消耗的 CPU 时间).
====Example 1-85. 使用 time 模块评价算法====[eg-1-85]
```
File: time-example-5.py
import time
def procedure():
time.sleep(2.5)
# measure process time
t0 = time.clock()
procedure()
print time.clock() - t0, "seconds process time"
# measure wall time
t0 = time.time()
procedure()
print time.time() - t0, "seconds wall time"
*B*0.0 seconds process time
2.50903499126 seconds wall time*b*
```
并不是所有的系统都能测量真实的进程时间. 一些系统中(包括 Windows ),
``clock`` 函数通常测量从程序启动到测量时的 wall time.
进程时间的精度受限制. 在一些系统中, 它超过 30 分钟后进程会被清理.
(原文: On many systems, it wraps around after just over 30 minutes.)
另参见 ``timing`` 模块( Windows 下的朋友不用忙活了,没有地~), 它可以测量两个事件之间的 wall time.