python标准库学习6
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 <Rectangle instance at 8c8260 > sized 100 x 100 create a blue <RoundedRectangle instance at 8c84c0 > 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" )) <function open at 794fa0 > 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 = > [] <built - in function len > = > [ '_ _doc_ _' , '_ _name_ _' , '_ _self_ _' ] <module 'sys' (built - in )> = > [ '_ _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 <built - in function callable > is callable <function dump at 8ca320 > is callable A is callable B is callable <unbound method A.method> is callable <A instance at 8caa10 > is * not * callable <B instance at 8cab00 > is callable <method A.method of B instance at 8cab00 > 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 < type 'int' > 1.0 = > 1.0 < type 'float' > 'string' = > string < type 'string' > 1.0 + 2.0 = > 3.0 < type 'float' > '*' * 10 = > * * * * * * * * * * < type 'string' > len ( 'world' ) = > 5 < type 'int' > 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 "<string>" , 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, "<script>" , "exec" ) print code exec code <code object ? at 8c6be0 , file "<script>" , line 0 > 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 ( "<HTTPError for %s: %s %s>" % ( 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: <HTTPError for http: / / www.python.org / foo: 200 Not Found> 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 importos importsys try: sys.exit(1) exceptSystemExit, value: print"caught exit(%s)"%value try: os._exit(2) exceptSystemExit, value: print"caught exit(%s)"%value print"bye!" caught exit(1) 本文转自被遗忘的博客园博客，原文链接：http://www.cnblogs.com/rollenholt/archive/2011/11/26/2264597.html，如需转载请自行联系原作者
