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<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()))
(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
<A instance at 796960> INSTANCE
<B instance at 796990> 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 "<Node %s at %x>" % (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