使用sys重定向输出

import sys

import string

class Redirect:

def _ _init_ _(self, stdout):

self.stdout = stdout

def write(self, s):

self.stdout.write(string.lower(s))

# redirect standard output (including the print statement)

# 重定向标准输出(包括print语句)

old_stdout = sys.stdout

sys.stdout = Redirect(sys.stdout)

print "HEJA SVERIGE",

print "FRISKT HUM\303\226R"

# restore standard output

# 恢复标准输出

sys.stdout = old_stdout

print "M\303\205\303\205\303\205\303\205L!"

heja sverige friskt hum\303\266r

M\303\205\303\205\303\205\303\205L!

使用sys模块退出程序

import sys

print "hello"

sys.exit(1)

print "there"

hello

注意sys.exit并不是立即退出. 而是引发一个SystemExit异常. 这意味着你可以在主程序中捕获对sys.exit的调用

捕获sys.exit调用

import sys

print "hello"

try:

sys.exit(1)

except SystemExit:

pass

print "there"

hello

there

如果准备在退出前自己清理一些东西(比如删除临时文件), 你可以配置一个 "退出处理函数"(exit handler), 它将在程序退出的时候自动被调用

另一种捕获sys.exit调用的方法

import sys

def exitfunc():

print "world"

sys.exitfunc = exitfunc

print "hello"

sys.exit(1)

print "there" # never printed # 不会被 print

hello

world

在 Python 2.0 以后, 你可以使用atexit模块来注册多个退出处理函数.

atexit 模块允许你注册一个或多个终止函数(暂且这么叫), 这些函数将在解释器终止前被自动调用.

调用 register 函数, 便可以将函数注册为终止函数,你也可以添加更多的参数, 这些将作为exit函数的参数传递.

使用 atexit 模块

import atexit

def exit(*args):

print "exit", args

# register two exit handler

atexit.register(exit)

atexit.register(exit, 1)

atexit.register(exit, "hello", "world")

exit ('hello', 'world')

exit (1,)

exit ()

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).

使用 time 模块获取当前时间

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)

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)

使用 time 模块格式化时间输出

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

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

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

使用 time.strptime 函数解析时间

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")

strptime 不完全实现

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[a-z]+)",

"%A": "(?P[a-z]+)",

"%b": "(?P[a-z]+)",

"%B": "(?P[a-z]+)",

"%C": "(?P\d\d?)",

"%d": "(?P\d\d?)",

"%D": "(?P\d\d?)/(?P\d\d?)/(?P\d\d)",

"%e": "(?P\d\d?)",

"%h": "(?P[a-z]+)",

"%H": "(?P\d\d?)",

"%I": "(?P\d\d?)",

"%j": "(?P\d\d?\d?)",

"%m": "(?P\d\d?)",

"%M": "(?P\d\d?)",

"%p": "(?Pam|pm)",

"%R": "(?P\d\d?):(?P\d\d?)",

"%S": "(?P\d\d?)",

"%T": "(?P\d\d?):(?P\d\d?):(?P\d\d?)",

"%U": "(?P\d\d)",

"%w": "(?P\d)",

"%W": "(?P\d\d)",

"%y": "(?P\d\d)",

"%Y": "(?P\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()))

(2000, 12, 20, 1, 2, 3, 0, 0, 0)

(2000, 11, 15, 12, 30, 45, 0, 0, 0)

使用 time 模块将本地时间元组转换为时间值(整数)

import time

t0 = time.time()

tm = time.localtime(t0)

print tm

print t0

print time.mktime(tm)

(1999, 9, 9, 0, 11, 8, 3, 252, 1)

936828668.16

936828668.0

将 UTC 时间元组转换为时间值(整数)

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)

(1999, 9, 8, 22, 12, 12, 2, 251, 0)

936828732.48

936828732

使用 time 模块评价算法

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"

0.0 seconds process time

2.50903499126 seconds wall time

使用 types 模块

import types

def check(object):

print object,

if type(object) is types.IntType:

print "INTEGER",

if type(object) is types.FloatType:

print "FLOAT",

if type(object) is types.StringType:

print "STRING",

if type(object) is types.ClassType:

print "CLASS",

if type(object) is types.InstanceType:

print "INSTANCE",

print

check(0)

check(0.0)

check("0")

class A:

pass

class B:

pass

check(A)

check(B)

a = A()

b = B()

check(a)

check(b)

0 INTEGER

0.0 FLOAT

0 STRING

A CLASS

B CLASS

INSTANCE

INSTANCE

使用 gc 模块收集循环引用垃圾

import gc

# create a simple object that links to itself

class Node:

def _ _init_ _(self, name):

self.name = name

self.parent = None

self.children = []

def addchild(self, node):

node.parent = self

self.children.append(node)

def _ _repr_ _(self):

return "" % (repr(self.name), id(self))

# set up a self-referencing structure

root = Node("monty")

root.addchild(Node("eric"))

root.addchild(Node("john"))

root.addchild(Node("michael"))

# remove our only reference

del root

print gc.collect(), "unreachable objects"

print gc.collect(), "unreachable objects"

12 unreachable objects

0 unreachable objects