python标准库学习6

wss1051

使用 apply 函数



def function(a, b):
print a, b
apply(function, ("whither", "canada?"))
apply(function, (1, 2 + 3))

　　

whither canada?
1 5
使用 apply 函数传递关键字参数



def function(a, b):
print a, b
apply(function, ("crunchy", "frog"))
apply(function, ("crunchy",), {"b": "frog"})
apply(function, (), {"a": "crunchy", "b": "frog"})
crunchy frog
crunchy frog
crunchy frog

　　

使用 apply 函数调用基类的构造函数



class Rectangle:
def _ _init_ _(self, color="white", width=10, height=10):
print "create a", color, self, "sized", width, "x", height
class RoundedRectangle(Rectangle):
def _ _init_ _(self, **kw):
apply(Rectangle._ _init_ _, (self,), kw)
rect = Rectangle(color="green", height=100, width=100)
rect = RoundedRectangle(color="blue", height=20)
create a green  sized 100 x 100
create a blue  sized 10 x 20

使用 _ _import_ _ 函数获得特定函数



def getfunctionbyname(module_name, function_name):
module = _ _import_ _(module_name)
return getattr(module, function_name)
print repr(getfunctionbyname("dumbdbm", "open"))


　　

使用 _ _import_ _ 函数实现 延迟导入



class LazyImport:
def _ _init_ _(self, module_name):
self.module_name = module_name
self.module = None
def _ _getattr_ _(self, name):
if self.module is None:
self.module = _ _import_ _(self.module_name)
return getattr(self.module, name)
string = LazyImport("string")
print string.lowercase
abcdefghijklmnopqrstuvwxyz

　　

使用 dir 函数



def dump(value):
print value, "=>", dir(value)
import sys
dump(0)
dump(1.0)
dump(0.0j) # complex number
dump([]) # list
dump({}) # dictionary
dump("string")
dump(len) # function
dump(sys) # module
0 => []
1.0 => []
0j => ['conjugate', 'imag', 'real']
[] => ['append', 'count', 'extend', 'index', 'insert',
'pop', 'remove', 'reverse', 'sort']
{} => ['clear', 'copy', 'get', 'has_key', 'items',
'keys', 'update', 'values']
string => []
=> ['_ _doc_ _', '_ _name_ _', '_ _self_ _']
=> ['_ _doc_ _', '_ _name_ _',
'_ _stderr_ _', '_ _stdin_ _', '_ _stdout_ _', 'argv',
'builtin_module_names', 'copyright', 'dllhandle',
'exc_info', 'exc_type', 'exec_prefix', 'executable',
...

　　

使用 dir 函数查找类的所有成员



class A:
def a(self):
pass
def b(self):
pass
class B(A):
def c(self):
pass
def d(self):
pass
def getmembers(klass, members=None):
# get a list of all class members, ordered by class
if members is None:
members = []
for k in klass._ _bases_ _:
getmembers(k, members)
for m in dir(klass):
if m not in members:
members.append(m)
return members
print getmembers(A)
print getmembers(B)
print getmembers(IOError)
['_ _doc_ _', '_ _module_ _', 'a', 'b']
['_ _doc_ _', '_ _module_ _', 'a', 'b', 'c', 'd']
['_ _doc_ _', '_ _getitem_ _', '_ _init_ _', '_ _module_ _', '_ _str_ _']

　　

使用 callable 函数



def dump(function):
if callable(function):
print function, "is callable"
else:
print function, "is *not* callable"
class A:
def method(self, value):
return value
class B(A):
def _ _call_ _(self, value):
return value
a = A()
b = B()
dump(0) # simple objects
dump("string")
dump(callable)
dump(dump) # function
dump(A) # classes
dump(B)
dump(B.method)
dump(a) # instances
dump(b)
dump(b.method)
0 is *not* callable
string is *not* callable
is callable
is callable
A is callable
B is callable
is callable
is *not* callable
is callable
is callable

　　

使用 eval 函数



def dump(expression):
result = eval(expression)
print expression, "=>", result, type(result)
dump("1")
dump("1.0")
dump("'string'")
dump("1.0 + 2.0")
dump("'*' * 10")
dump("len('world')")
1 => 1
1.0 => 1.0
'string' => string
1.0 + 2.0 => 3.0
'*' * 10 => **********
len('world') => 5

　　

使用 eval 函数执行任意命令



print eval("_ _import_ _('os').getcwd()")
print eval("_ _import_ _('os').remove('file')")
/home/fredrik/librarybook
Traceback (innermost last):
File "builtin-eval-example-2", line 2, in ?
File "", line 0, in ?
os.error: (2, 'No such file or directory')

　　

使用 compile 函数检查语法



NAME = "script.py"
BODY = """
prnt 'owl-stretching time'
"""
try:
compile(BODY, NAME, "exec")
except SyntaxError, v:
print "syntax error:", v, "in", NAME
# syntax error: invalid syntax in script.py

　　



执行已编译的代码

　　



BODY = """
print 'the ant, an introduction'
"""
code = compile(BODY, "", "exec")
print code
exec code

the ant, an introduction

　　Python 还提供了 execfile 函数, 一个从文件加载代码, 编译代码, 执行代码的快捷方式.

使用 execfile 函数



execfile("hello.py")
def EXECFILE(filename, locals=None, globals=None):
exec compile(open(filename).read(), filename, "exec") in locals, globals
EXECFILE("hello.py")
hello again, and welcome to the show
hello again, and welcome to the show

　　

显式地访问 _ _builtin_ _ 模块中的函数



def open(filename, mode="rb"):
import _ _builtin_ _
file = _ _builtin_ _.open(filename, mode)
if file.read(5) not in("GIF87", "GIF89"):
raise IOError, "not a GIF file"
file.seek(0)
return file
fp = open("samples/sample.gif")
print len(fp.read()), "bytes"
fp = open("samples/sample.jpg")
print len(fp.read()), "bytes"
3565 bytes
Traceback (innermost last):
File "builtin-open-example-1.py", line 12, in ?
File "builtin-open-example-1.py", line 5, in open
IOError: not a GIF file

　　

使用 exceptions 模块



# python imports this module by itself, so the following
# line isn't really needed
# python 会自动导入该模块, 所以以下这行是不必要的
# import exceptions
class HTTPError(Exception):
# indicates an HTTP protocol error
def _ _init_ _(self, url, errcode, errmsg):
self.url = url
self.errcode = errcode
self.errmsg = errmsg
def _ _str_ _(self):
return (
"" %
(self.url, self.errcode, self.errmsg)
)
try:
raise HTTPError("http://www.python.org/foo", 200, "Not Found")
except HTTPError, error:
print "url", "=>", error.url
print "errcode", "=>", error.errcode
print "errmsg", "=>", error.errmsg
raise # reraise exception
url => http://www.python.org/foo
errcode => 200
errmsg => Not Found
Traceback (innermost last):
File "exceptions-example-1", line 16, in ?
HTTPError:

　　

使用 os 模块重命名和删除文件



import os
import string
def replace(file, search_for, replace_with):
# replace strings in a text file
back = os.path.splitext(file)[0] + ".bak"
temp = os.path.splitext(file)[0] + ".tmp"
try:
# remove old temp file, if any
os.remove(temp)
except os.error:
pass
fi = open(file)
fo = open(temp, "w")
for s in fi.readlines():
fo.write(string.replace(s, search_for, replace_with))
fi.close()
fo.close()
try:
# remove old backup file, if any
os.remove(back)
except os.error:
pass
# rename original to backup...
os.rename(file, back)
# ...and temporary to original
os.rename(temp, file)
#
# try it out!
file = "samples/sample.txt"
replace(file, "hello", "tjena")
replace(file, "tjena", "hello")

　　

使用 os 列出目录下的文件



import os
for file in os.listdir("samples"):
print file
sample.au
sample.jpg
sample.wav
...

　　getcwd 和 chdir 函数分别用于获得和改变当前工作目录

使用 os 模块改变当前工作目录



import os
# where are we?
cwd = os.getcwd()
print "1", cwd
# go down
os.chdir("samples")
print "2", os.getcwd()
# go back up
os.chdir(os.pardir)
print "3", os.getcwd()
1 /ematter/librarybook
2 /ematter/librarybook/samples
3 /ematter/librarybook

　　makedirs 和 removedirs 函数用于创建或删除目录层

使用 os 模块创建/删除多个目录级



import os
os.makedirs("test/multiple/levels")
fp = open("test/multiple/levels/file", "w")
fp.write("inspector praline")
fp.close()
# remove the file
os.remove("test/multiple/levels/file")
# and all empty directories above it
os.removedirs("test/multiple/levels")

　　removedirs 函数会删除所给路径中最后一个目录下所有的空目录. 而 mkdir 和 rmdir 函数只能处理单个目录级

使用 os 模块创建/删除目录



import os
os.mkdir("test")
os.rmdir("test")
os.rmdir("samples") # this will fail
Traceback (innermost last):
File "os-example-7", line 6, in ?
OSError: [Errno 41] Directory not empty: 'samples'

　　如果需要删除非空目录, 你可以使用 shutil 模块中的 rmtree 函数



>>> import shutil
shutil.rmtree("d:\\a")

　　复制文件目录（包括内部文件）



>>> shutil.copytree("d:\\new","d:\\a")

　　复制文件操作：



shutil.copyfile("d:\\new\\a.txt","d:\\a.txt")

　　目录或文件的移动操作



shutil.move("d:\\new\\a.txt","d:\\")

　　

使用 os 模块获取文件属性



import os
import time
file = "samples/sample.jpg"
def dump(st):
mode, ino, dev, nlink, uid, gid, size, atime, mtime, ctime = st
print "- size:", size, "bytes"
print "- owner:", uid, gid
print "- created:", time.ctime(ctime)
print "- last accessed:", time.ctime(atime)
print "- last modified:", time.ctime(mtime)
print "- mode:", oct(mode)
print "- inode/dev:", ino, dev
#
# get stats for a filename
st = os.stat(file)
print "stat", file
dump(st)
print
#
# get stats for an open file
fp = open(file)
st = os.fstat(fp.fileno())
print "fstat", file
dump(st)
stat samples/sample.jpg
- size: 4762 bytes
- owner: 0 0
- created: Tue Sep 07 22:45:58 1999
- last accessed: Sun Sep 19 00:00:00 1999
- last modified: Sun May 19 01:42:16 1996
- mode: 0100666
- inode/dev: 0 2
fstat samples/sample.jpg
- size: 4762 bytes
- owner: 0 0
- created: Tue Sep 07 22:45:58 1999
- last accessed: Sun Sep 19 00:00:00 1999
- last modified: Sun May 19 01:42:16 1996
- mode: 0100666
- inode/dev: 0 0

　　可以使用 chmod 和 utime 函数修改文件的权限模式和时间属性

使用 os 模块修改文件的权限和时间戳



import os
import stat, time
infile = "samples/sample.jpg"
outfile = "out.jpg"
# copy contents
fi = open(infile, "rb")
fo = open(outfile, "wb")
while 1:
s = fi.read(10000)
if not s:
break
fo.write(s)
fi.close()
fo.close()
# copy mode and timestamp
st = os.stat(infile)
os.chmod(outfile, stat.S_IMODE(st[stat.ST_MODE]))
os.utime(outfile, (st[stat.ST_ATIME], st[stat.ST_MTIME]))
print "original", "=>"
print "mode", oct(stat.S_IMODE(st[stat.ST_MODE]))
print "atime", time.ctime(st[stat.ST_ATIME])
print "mtime", time.ctime(st[stat.ST_MTIME])
print "copy", "=>"
st = os.stat(outfile)
print "mode", oct(stat.S_IMODE(st[stat.ST_MODE]))
print "atime", time.ctime(st[stat.ST_ATIME])
print "mtime", time.ctime(st[stat.ST_MTIME])
original =>
mode 0666
atime Thu Oct 14 15:15:50 1999
mtime Mon Nov 13 15:42:36 1995
copy =>
mode 0666
atime Thu Oct 14 15:15:50 1999
mtime Mon Nov 13 15:42:36 1995

　　system 函数在当前进程下执行一个新命令, 并等待它完成

使用 os 执行操作系统命令



import os
if os.name == "nt":
command = "dir"
else:
command = "ls -l"
os.system(command)
-rwxrw-r--   1 effbot  effbot        76 Oct  9 14:17 README
-rwxrw-r--   1 effbot  effbot      1727 Oct  7 19:00 SimpleAsyncHTTP.py
-rwxrw-r--   1 effbot  effbot       314 Oct  7 20:29 aifc-example-1.py
-rwxrw-r--   1 effbot  effbot       259 Oct  7 20:38 anydbm-example-1.py
...

　　命令通过操作系统的标准 shell 执行, 并返回 shell 的退出状态. 需要注意的是在 Windows 下, shell 通常是 command.com , 它的推出状态总是 0.
　　

　　exec 函数会使用新进程替换当前进程(或者说是"转到进程").

使用 os 模块启动新进程



import os
import sys
program = "python"
arguments = ["hello.py"]
print os.execvp(program, (program,) +  tuple(arguments))
print "goodbye"
hello again, and welcome to the show

　　execvp 函数, 它会从标准路径搜索执行程序, 把第二个参数(元组)作为单独的参数传递给程序, 并使用当前的环境变量来运行程序. 其他七个同类型函数请参阅 Python Library Reference .
　　在 Unix 环境下, 你可以通过组合使用 exec , fork 以及 wait 函数来从当前程序调用另一个程序,fork 函数复制当前进程, wait 函数会等待一个子进程执行结束.

使用 os 模块调用其他程序 (Unix)



import os
import sys
def run(program, *args):
pid = os.fork()
if not pid:
os.execvp(program, (program,) +  args)
return os.wait()[0]
run("python", "hello.py")
print "goodbye"
hello again, and welcome to the show
goodbye

　　
　　fork 函数在子进程返回中返回 0 (这个进程首先从 fork 返回值), 在父进程中返回一个非 0 的进程标识符(子进程的 PID ). 也就是说, 只有当我们处于子进程的时候 "not pid" 才为真.
　　fork 和 wait 函数在 Windows 上是不可用的, 但是你可以使用 spawn 函数不过, spawn 不会沿着路径搜索可执行文件, 你必须自己处理好这些.

或许系统当前的“PATH”变量的值



>>> import string
>>>import os
>>> for path in string.split(os.environ["PATH"],os.pathsep):
print path

C:\Program Files\NVIDIA Corporation\PhysX\Common
d:\program files\Python27\Lib\site-packages\PyQt4
C:\windows\system32
C:\windows
C:\windows\System32\Wbem
C:\windows\System32\WindowsPowerShell\v1.0\
C:\Program Files\Common Files\Thunder Network\KanKan\Codecs
D:\Program Files\python
D:\Program Files\Java\jdk1.6.0_23/bin
D:\Program Files\Java\jdk1.6.0_23/jre/bin
C:\Program Files\Microsoft SQL Server\90\Tools\binn\
D:\vs2010-qt-src-4.7.4\qt-src-4.7.4\bin
C:\Program Files\Intel\WiFi\bin\
C:\Program Files\Common Files\Intel\WirelessCommon\
C:\Program Files\Lenovo\Bluetooth Software\
D:\vs2010-qt-src-4.7.4\qt-src-4.7.4\bin
D:\vs2010-qt-src-4.7.4\qt-src-4.7.4\lib
D:\vs2010-qt-src-4.7.4\qt-src-4.7.4\include
D:\Qt\4.7.4\bin
>>>

　　

使用 os 模块调用其他程序 (Windows)



import os
import string
def run(program, *args):
# find executable
for path in string.split(os.environ["PATH"], os.pathsep):
file = os.path.join(path, program) + ".exe"
try:
return os.spawnv(os.P_WAIT, file, (file,) + args)
except os.error:
pass
raise os.error, "cannot find executable"
run("python", "hello.py")
print "goodbye"
hello again, and welcome to the show
goodbye

　　spawn 函数还可用于在后台运行一个程序.下面这个例子给 run 函数添加了一个可选的 mode 参数; 当设置为 os.P_NOWAIT 时, 这个脚本不会等待子程序结束, 默认值 os.P_WAIT 时 spawn 会等待子进程结束.
　　其它的标志常量还有 os.P_OVERLAY ,它使得 spawn 的行为和 exec 类似, 以及 os.P_DETACH , 它在后台运行子进程, 与当前控制台和键盘焦点隔离.



import os
import string
def run(program, *args, **kw):
# find executable
mode = kw.get("mode", os.P_WAIT)
for path in string.split(os.environ["PATH"], os.pathsep):
file = os.path.join(path, program) + ".exe"
try:
return os.spawnv(mode, file, (file,) + args)
except os.error:
pass
raise os.error, "cannot find executable"
run("python", "hello.py", mode=os.P_NOWAIT)
print "goodbye"
goodbye
hello again, and welcome to the show

　　下面这个例子提供了一个在 Unix 和 Windows 平台上通用的 spawn 方法

使用 spawn 或 fork/exec 调用其他程序



import os
import string
if os.name in ("nt", "dos"):
exefile = ".exe"
else:
exefile = ""
def spawn(program, *args):
try:
# possible 2.0 shortcut!
return os.spawnvp(program, (program,) + args)
except AttributeError:
pass
try:
spawnv = os.spawnv
except AttributeError:
# assume it's unix
pid = os.fork()
if not pid:
os.execvp(program, (program,) + args)
return os.wait()[0]
else:
# got spawnv but no spawnp: go look for an executable
for path in string.split(os.environ["PATH"], os.pathsep):
file = os.path.join(path, program) + exefile
try:
return spawnv(os.P_WAIT, file, (file,) + args)
except os.error:
pass
raise IOError, "cannot find executable"
#
# try it out!
spawn("python", "hello.py")
print "goodbye"
hello again, and welcome to the show
goodbye

　　

处理守护进程
　　Unix 系统中, 你可以使用 fork 函数把当前进程转入后台(一个"守护者/daemon"). 一般来说, 你需要派生(fork off)一个当前进程的副本, 然后终止原进程

使用 os 模块使脚本作为守护执行 (Unix)



import os
import time
pid = os.fork()
if pid:
os._exit(0) # kill original
print "daemon started"
time.sleep(10)
print "daemon terminated"

　　

使用 os 模块终止当前进程



import os
import sys
try:
sys.exit(1)
except SystemExit, value:
print "caught exit(%s)" % value
try:
os._exit(2)
except SystemExit, value:
print "caught exit(%s)" % value
print "bye!"
caught exit(1)