python标准库学习8

最新推荐文章于 2021-06-16 11:11:38 发布

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最新推荐文章于 2021-06-16 11:11:38 发布

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文章标签： python

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