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4,700 | self text 'def write(selfstring)self text +string def writelines(selflines)for line in linesself write(lineempty string when created add string of bytes add each line in list class inputsimulated input file def __init__(selfinput='')default argument self text input save string when created def read(selfsize=none)option... |
4,701 | directlythe function reads from the keyboard and writes to the screenjust as if it were run as program without redirectionc:\pp \system\streamspython from teststreams import interact interact(hello stream world enter number> squared is enter number> squared is enter number^ bye nowlet' run this function under the contr... |
4,702 | enter number>bye this is an artificial exampleof coursebut the techniques illustrated are widely applicable for instanceit' straightforward to add gui interface to program written to interact with command-line user simply intercept standard output with an object such as the output class instance shown earlier and throw... |
4,703 | buff getvalue(' spam \nrestore original stream note that there is also an io bytesio class with similar behaviorbut which maps file operations to an in-memory bytes bufferinstead of str stringfrom io import bytesio stream bytesio(stream write( 'spam'stream getvalue( 'spamstream bytesio( 'dpam'stream read( 'dpamdue to t... |
4,704 | return to the original output stream (as shown in the section on redirecting streams to objectsfor exampleimport sys print('spam file=sys stderrwill send text the standard error stream object rather than sys stdout for the duration of this single print call only the next normal print statement (without fileprints to st... |
4,705 | in factby passing in the desired mode flagwe redirect either spawned program' output or input streams to file in the calling scriptsand we can obtain the spawned program' exit status code from the close method (none means "no errorhereto illustrateconsider the following two scriptsc:\pp \system\streamstype hello-out py... |
4,706 | for even more control over the streams of spawned programswe can employ the subprocess module we introduced in the preceding as we learned earlierthis module can emulate os popen functionalitybut it can also achieve feats such as bidirectional stream communication (accessing both program' input and outputand tying the ... |
4,707 | this module let' reuse the simple writer and reader scripts we wrote earlier to demonstratec:\pp \system\streamstype writer py print("helphelpi' being repressed!"print( :\pp \system\streamstype reader py print('got this"% "input()import sys data sys stdin readline()[:- print('the meaning of life is'dataint(data code li... |
4,708 | (and not bothprevents us from catching the second script' output in our codeimport os os popen('python writer py'' ' os popen('python reader py'' ' writep read( close(got this"helphelpi' being repressed!the meaning of life is print(xnone from the broader perspectivethe os popen call and subprocess module are python' po... |
4,709 | if you are familiar with other common shell script languagesit might be useful to see how python compares here is simple script in unix shell language called csh that mails all the files in the current working directory with suffix of py ( all python source filesto hopefully fictitious address#!/bin/csh foreach (pyecho... |
4,710 | file and directory tools "erase your hard drive in five easy steps!this continues our look at system interfaces in python by focusing on file and directory-related tools as you'll seeit' easy to process files and directory trees with python' built-in and standard library support because files are part of the core pytho... |
4,711 | related to database topicsaddressed in in this sectionwe'll take brief tutorial look at the built-in file object and explore handful of more advanced file-related topics as usualyou should consult either python' library manual or reference books such as python pocket reference for further details and methods we don' ha... |
4,712 | distinction when using system tools like pipe descriptors and socketsbecause they transfer data as byte strings today (though their content can be decoded and encoded as unicode text if neededmoreoverbecause text-mode files require that content be decodable per unicode encoding schemeyou must read undecodable file cont... |
4,713 | we'll sometimes omit in this book to save space)and as we'll seeclose calls are often optionalunless you need to open and read the file again during the same program or sessionc:\temppython file open('data txt'' 'file write('hello file world!\ ' file write('bye file world \ ' file close(open output file objectcreates w... |
4,714 | iteration tool)but it is convenient in scripts that save output in list to be written later closing the file close method used earlier finalizes file contents and frees up system resources for instanceclosing forces buffered output data to be flushed out to disk normallyfiles are automatically closed when the file obje... |
4,715 | finally clause is the most generalsince it allows you to provide general exit actions for any type of exceptionsmyfile open(filename' 'tryprocess myfile finallymyfile close(in recent python releasesthoughthe with statement provides more concise alternative for some specific objects and exit actionsincluding closing fil... |
4,716 | actions are automatically run to close the filesregardless of exception outcomeswith open('data'as finopen('results'' 'as foutfor line in finfout write(transform(line)context manager-dependent code like this seems to have become more common in recent yearsbut this is likely at least in part because newcomers are accust... |
4,717 | seek( call is used here before each test to rewind the file to its beginning (more on this call in moment)file seek( file read('hello file world!\nbye file world \nfile seek( file readlines(['hello file world!\ ''bye file seek( file readline('hello file world!\nfile readline('bye file world \nfile readline('file seek( ... |
4,718 | in older versions of pythonthe traditional way to read file line by line in for loop was to read the file into list that could be stepped through as usualfile open('data txt'for line in file readlines()print(lineend=''don' do this anymoreif you've already studied the core language using first book like learning pythony... |
4,719 | 'bye file world \nfile __next__(traceback (most recent call last)file ""line in stopiteration interestinglyiterators are automatically used in all iteration contextsincluding the list constructor calllist comprehension expressionsmap callsand in membership checksopen('data txt'readlines(['hello file world!\ ''bye file ... |
4,720 | needshere are few things you should know about these three open argumentsfilename as mentioned earlierfilenames can include an explicit directory path to refer to files in arbitrary places on your computerif they do notthey are taken to be names relative to the current working directory (described in the prior in gener... |
4,721 | all of the preceding examples process simple text filesbut python scripts can also open and process files containing binary data--jpeg imagesaudio clipspacked binary data produced by fortran and programsencoded textand anything else that can be stored in files as bytes the primary difference in terms of your code is th... |
4,722 | open('data bin''wb'write('spam\ 'typeerrormust be bytes or buffernot str but notice that this file' line ends with just \ninstead of the windows \ \ that showed up in the preceding example for the text file in binary mode strictly speakingbinary mode disables unicode encoding translationbut it also prevents the automat... |
4,723 | sys getdefaultencodingcontinuing our interactive sessionopen('data txt'' 'encoding='latin 'write(data open('data txt'' 'encoding='latin 'read('spamopen('data txt''rb'read( 'sp\xe mif we open in binary modethoughno encoding translation occurs--the last command in the preceding example shows us what' actually stored on t... |
4,724 | '\xa \ \ \ \ %\ \ \ \ %if all your text is ascii you generally can ignore encoding altogetherdata in files maps directly to characters in stringsbecause ascii is subset of most platformsdefault encodings if you must process files created with other encodingsand possibly on different platforms (obtained from the webfor ... |
4,725 | random \ in data might be dropped on inputor added for \ in the data on output the net effect is that your binary data would be trashed when read and written-probably not quite what you want for your audio files and imagesthis issue has become almost secondary in python xbecause we generally cannot use binary data with... |
4,726 | open('temp bin''rb'read( ' \ \rc\ \ \ndopen('temp bin'' 'read(' \ \nc\ \ndtext mode writeadded \ again dropsalters \ on input the short story to remember here is that you should generally use \ to refer to endline in all your text file contentand you should always open binary data in binary file modes to suppress both ... |
4,727 | contentsthe standard library struct module is more powerful alternative the struct module provides calls to pack and unpack binary dataas though the data was laid out in -language struct declaration it is also capable of composing and decomposing using any endian-ness you desire (endian-ness determines whether the most... |
4,728 | number '\ \ struct unpack('> 'number( ,packed binary data crops up in many contextsincluding some networking tasksand in data produced by other programming languages because it' not part of every programming job' descriptionthoughwe'll defer to the struct module' entry in the python library manual for more details rand... |
4,729 | records [ 'ssssssss' 'pppppppp' 'aaaaaaaa' 'mmmmmmmm'file open('random bin'' + 'for rec in recordssize file write(recfile flush(pos file seek( print(file read() 'ssssssssppppppppaaaaaaaammmmmmmmwrite four records bytes for binary mode read entire file nowlet' reopen our file in + modethis mode allows both reads and wri... |
4,730 | file open('random bin''rb'file seek(reclen file read(reclenb'yyyyyyyybinary mode works the same here fetch record returns byte strings but unless your file' content is always simple unencoded text form like ascii and has no translated line-endstext mode should not generally be used if you are going to seek--line-ends m... |
4,731 | moves to position in the file technicallyos calls process files by their descriptorswhich are integer codes or "handlesthat identify files in the operating system descriptor-based files deal in raw bytesand have no notion of the line-end or unicode translations for text that we studied in the prior section in factapart... |
4,732 | file write('hello stdio file\ 'file flush(fd file fileno(fd import os os write(fdb'hello descriptor file\ 'file close(create external fileobject write via file object method else os write to disk firstget descriptor from object :\temptype spam txt hello stdio file hello descriptor file lines from both schemes write via... |
4,733 | access (o_excland nonblocking modes (o_nonblockwhen file is opened some of these flags are not portable across platforms (another reason to use built-in file objects most of the time)see the library manual or run dir(oscall on your machine for an exhaustive list of other open flags available one final note hereusing os... |
4,734 | objfile read('jello stdio file\nhello descriptor file\nobjfile os fdopen(fdfile' 'encoding='latin 'closefd=trueobjfile seek( objfile read('jello stdio file\nhello descriptor file\nwe'll make use of this file object wrapper technique to simplify text-oriented pipes and other descriptor-like objects later in this book ( ... |
4,735 | + for \ added import os info os stat( ' :\temp\spam txt'info nt stat_result(st_mode= st_ino= st_dev= st_nlink= st_uid= st_gid= st_size= st_atime= st_mtime= st_ctime= info st_modeinfo st_size ( via named-tuple item attr names import stat info[stat st_mode]info[stat st_sizevia stat module presets ( stat s_isdir(info st_m... |
4,736 | and put it in directory on the module search pathwe can use it any time we need to step through file line by line example - is client script that does simple line translations example - pp \system\filetools\commands py #!/usr/local/bin/python from sys import argv from scanfile import scanner class unknowncommand(except... |
4,737 | things up by shifting processing from python code to built-in tools for instanceif we're concerned with speedwe can probably make our file scanner faster by using the file' line iterator to step through the file instead of the manual readline loop in example - (though you' have to time this with your python to be sure)... |
4,738 | lines here in the file-based filter of example - and also guarantee immediate file closures if the processing function fails with an exceptiondef filter_files(namefunction)with open(name' 'as inputopen(name out'' 'as outputfor line in inputoutput write(function(line)write the modified line and againfile object line ite... |
4,739 | it onit will work regardless of which other tools are available thereall you need is python moreovercoding such tasks in python also allows you to perform arbitrary actions along the way--replacementsdeletionsand whatever else you can code in the python language walking one directory the most common way to go about wri... |
4,740 | spawning the appropriate platform-specific command line and reading its output (the text normally thrown up on the console window) :\temppython import os os popen('dir / 'readlines(['parts\ ''pp \ ''random bin\ ''spam txt\ ''temp bin\ ''temp txt\ 'lines read from shell command come back with trailing end-of-line charac... |
4,741 | list(os popen( ' :\cygwin\bin\ls parts/part*')['parts/part \ ''parts/part \ ''parts/part \ ''parts/part \ 'the next two alternative techniques do better on both counts the glob module the term globbing comes from the wildcard character in filename patternsper computing folklorea matches "globof characters in less poeti... |
4,742 | pp \examples\pp \lang\summer py pp \examples\pp \pytools\search_all py herewe get back filenames from two different directories that match the spy patternbecause the directory name preceding this is wildcardpython collects all possible ways to reach the base filenames using os popen to spawn shell commands achieves the... |
4,743 | in the last examplei pointed out that glob returns names with directory pathswhereas listdir gives raw base filenames for convenient processingscripts often need to split glob results into base files or expand listdir results into full paths such translations are easy if we let the os path module do all the work for us... |
4,744 | directory we can either write recursive routine to traverse the treeor use treewalker utility built into the os module such tools can be used to searchcopycompareand otherwise process arbitrary directory trees on any platform that python runs on (and that' just about everywherethe os walk visitor to make it easy to app... |
4,745 | "list file tree with os walkimport sysos def lister(root)for (thisdirsubsherefilesherein os walk(root)print('[thisdir ']'for fname in filesherepath os path join(thisdirfnameprint(pathif __name__ ='__main__'lister(sys argv[ ]for root dir generate dirs in tree print files in this dir add dir name prefix dir name in cmdli... |
4,746 | of their names and which contain the search string when match is foundits full name is appended to the results list objectalternativelywe could also simply build list of all py files and search each in for loop after the walk since we're going to code much more general solution to this type of problem in thoughwe'll le... |
4,747 | list files in dir tree by recursion import sysos def mylister(currdir)print('[currdir ']'for file in os listdir(currdir)path os path join(currdirfileif not os path isdir(path)print(pathelsemylister(pathif __name__ ='__main__'mylister(sys argv[ ]list files here add dir path back recur into subdirs dir name in cmdline as... |
4,748 | modes in xgiven bytes argumentthis function will return filenames as encoded byte stringsgiven normal str string argumentit instead returns filenames as unicode stringsdecoded per the filesystem' encoding schemec:\pp \system\filetoolspython import os os listdir(')[: ['bigext-tree py''bigpy-dir py''bigpy-path py''bigpy-... |
4,749 | latin- but may contain files with arbitrarily encoded names from cross-machine copiesthe weband so on depending upon contextexception handlers may be used to suppress some types of encoding errors as well we'll see an example of how this can matter in the first section of where an undecodable directory name generates a... |
4,750 | if it might be outside the platform defaultand you should rely on the default unicode api for file names in most cases againsee python' manuals for more on the unicode file name story than we have space to cover fully hereand see learning pythonfourth editionfor more on unicode in general in we're going to put the tool... |
4,751 | parallel system tools "telling the monkeys what to domost computers spend lot of time doing nothing if you start system monitor tool and watch the cpu utilizationyou'll see what mean--it' rare to see one hit percenteven when you are running multiple programs there are just too many delays built into softwaredisk access... |
4,752 | to screen redrawsmouse clicksand so on parallel processing comes to the rescue heretoo by performing such long-running tasks in parallel with the rest of the programthe system at large can remain responsive no matter how busy some of its parts may be moreoverthe parallel processing model is natural fit for structuring ... |
4,753 | forked processes are traditional way to structure parallel tasksand they are fundamental part of the unix tool set forking is straightforward way to start an independent programwhether it is different from the calling program or not forking is based on the notion of copying programswhen program calls the fork routineth... |
4,754 | scriptfor instanceruns the child function in child processes only because forking is ingrained in the unix programming modelthis script works well on unixlinuxand modern macs unfortunatelythis script won' work on the standard version of python for windows todaybecause fork is too much at odds with the windows model pyt... |
4,755 | example - pp \system\processes\fork-count py ""fork basicsstart copies of this program running in parallel with the originaleach copy counts up to on the same stdout stream--forks copy process memoryincluding file descriptorsfork doesn' currently work on windows without cygwinuse os spawnv or multiprocessing on windows... |
4,756 | [ = more output omitted the output of all of these processes shows up on the same screenbecause all of them share the standard output stream (and system prompt may show up along the waytootechnicallya forked process gets copy of the original process' global memoryincluding open file descriptors because of thatglobal ob... |
4,757 | the arguments to os execlp specify the program to be run by giving command-line arguments used to start the program ( what python scripts know as sys argvif successfulthe new program begins running and the call to os execlp itself never returns (since the original program has been replacedthere' really nothing to retur... |
4,758 | just as when typed at shellthe string of arguments passed to os execlp by the forkexec script in example - starts another python program fileas shown in example - example - pp \system\processes\child py import ossys print('hello from child'os getpid()sys argv[ ]here is this code in action on linux it doesn' look much d... |
4,759 | as mentionedthe os fork call is present in the cygwin version of python on windows even though this call is missing in the standard version of python for windowsyou can fork processes on windows with python if you install and use cygwin howeverthe cygwin fork call is not as efficient and does not work exactly the same ... |
4,760 | official python was still python to get python under cygwinit had to be built from its source code if this is still required when you read thismake sure you have gcc and make installed on your cygwinthen fetch python' source code package from python orgunpack itand build python with the usual commands/configure make ma... |
4,761 | components such as imported modules are shared among all threads in programif one thread assigns global variablefor instanceits new value will be seen by other threads some care must be taken to control access to shared itemsbut to some this seems generally simpler to use than the process communication tools necessary ... |
4,762 | realistic threaded programs are usually structured as one or more producer ( workerthreads that add data to queuealong with one or more consumer threads that take the data off the queue and process it in typical threaded guifor exampleproducers may download or compute data and place it on the queuethe consumer--the mai... |
4,763 | for synchronizing access to shared objects with locks this book presents both the _thread and threading modulesand its examples use both interchangeably some python users would recommend that you always use threading rather than _thread in general in factthe latter was renamed from thread to _thread in to suggest such ... |
4,764 | def parent() while truei + _thread start_new_thread(child( ,)if input(=' 'break parent(this script really contains only two thread-specific linesthe import of the _thread module and the thread creation call to start threadwe simply call the _thread start_new_thread functionno matter what platform we're programming on +... |
4,765 | started other ways to code threads with _thread although the preceding script runs simple functionany callable object may be run in the threadbecause all threads live in the same process for instancea thread can also run lambda function or bound method of an object (the following code is part of file thread-alts py in ... |
4,766 | thread outputs may be intermixed in this version arbitrarily ""import _thread as threadtime def counter(myidcount)for in range(count)time sleep( print('[% =% (myidi)function run in threads for in range( )thread start_new_thread(counter( )spawn threads each thread loops times time sleep( print('main thread exiting 'don'... |
4,767 | [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = more output omitted main thread exiting if this looks oddit' because it should in factthis demonstrates probably the most unusual aspect of threads what' happening here is that the output of the threads run in parallel is interm... |
4,768 | the work done so far by another whose operations are still in progress the extent to which this becomes an issue varies per applicationand sometimes it isn' an issue at all but even things that aren' obviously at risk may be at risk files and streamsfor exampleare shared by all threads in programif multiple threads wri... |
4,769 | access to the stdout stream hencethe output of this script is similar to that of the original versionexcept that standard output text is never mangled by overlapping printsc:\pp \system\threadsthread-count-mutex py [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = main ... |
4,770 | ""uses mutexes to know when threads are done in parent/main threadinstead of time sleeplock stdout to avoid comingled prints""import _thread as thread stdoutmutex thread allocate_lock(exitmutexes [thread allocate_lock(for in range( )def counter(myidcount)for in range(count)stdoutmutex acquire(print('[% =% (myidi)stdout... |
4,771 | def counter(myidcount)for in range(count)stdoutmutex acquire(print('[% =% (myidi)stdoutmutex release(exitmutexes[myidtrue signal main thread for in range( )thread start_new_thread(counter( )while false in exitmutexespass print('main thread exiting 'the output of this script is similar to the prior-- threads counting to... |
4,772 | global scope might be more coherenttoo when passed inall threads reference the same objectbecause they are all part of the same process reallythe process' object memory is shared memory for threadsregardless of how objects in that shared memory are referenced (whether through global scope variablespassed argument names... |
4,773 | [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = [ = main thread exiting of coursethreads are for much more than counting we'll put shared global data to more practical use in "adding user interfaceon page where it will serve as completion signals from child processing threads transferring data over network to main ... |
4,774 | def __init__(selfmyidcountmutex)self myid myid self count count self mutex mutex threading thread __init__(selfsubclass thread object per-thread state information shared objectsnot globals def run(self)run provides thread logic for in range(self count)still sync stdout access with self mutexprint('[% =% (self myidi)std... |
4,775 | the advantage of taking this more coding-intensive route is that we get both per-thread state information (the usual instance attribute namespace)and set of additional thread-related tools from the framework "for free the thread join method used near the end of this scriptfor instancewaits until the thread exits (by de... |
4,776 | stateor can leverage any of oop' many benefits in general your thread classes don' necessarily have to subclass threadthough in factjust as in the _thread modulethe thread' target in threading may be any type of callable object when combined with techniques such as bound methods and nested scope referencesthe choice be... |
4,777 | "prints different results on different runs on windows import threadingtime count def adder()global count count count time sleep( count count update shared name in global scope threads share object memory and global names threads [for in range( )thread threading thread(target=adderargs=()thread start(threads append(thr... |
4,778 | with addlockcount count time sleep( with addlockcount count auto acquire/release around stmt only thread updating at once addlock threading lock(threads [for in range( )thread threading thread(target=adderargs=(addlock,)thread start(threads append(threadfor thread in threadsthread join(print(countalthough some basic op... |
4,779 | data structure-- first-in first-out (fifolist of python objectsin which items are added on one end and removed from the other like normal liststhe queues provided by this module may contain any type of python objectincluding both simple types (stringslistsdictionariesand so onand more exotic types (class instancesarbit... |
4,780 | time sleep(((numproducers- nummessages print('main thread exit 'before show you this script' outputi want to highlight few points in its code arguments versus globals notice how the queue is assigned to global variablebecause of thatit is shared by all of the spawned threads (all of them run in the same process and in ... |
4,781 | worker threads to finish their tasks in the absence of join calls or sleepsbut it can prevent programs like the one in example - from shutting down when they wish to make this example work with threadinguse the following alternative code (see queuetest py in the examples tree for complete version of thisas well as thre... |
4,782 | consumer got =[producer id= count= consumer got =[producer id= count= consumer got =[producer id= count= consumer got =[producer id= count= consumer got =[producer id= count= consumer got =[producer id= count= main thread exit try adjusting the parameters at the top of this script to experiment with different scenarios... |
4,783 | as processesthe efficiency and shared-state model of threads make them ideal for this role moreoversince most gui toolkits do not allow multiple threads to update the gui in parallelupdates are best restricted to the main thread because only the main thread should generally update the displaygui programs typically take... |
4,784 | example in later in this we'll also meet the multiprocessing modulewhose process and queue support offers new options for implementing this gui model using processes instead of threadsas suchthey work around the limitations of the thread gilbut may incur extra performance overheads that can vary per platformand may not... |
4,785 | although it' lower-level topic than you generally need to do useful thread work in pythonthe implementation of python' threads can have impacts on both performance and coding this section summarizes implementation details and some of their ramifications threads implementation in the upcoming python this section describ... |
4,786 | than one thread might attempt to update the same variable at the same timethe threads should generally be given exclusive access to the object with locks otherwiseit' not impossible that thread switches will occur in the middle of an update statement' bytecode locks are not strictly required for all shared object acces... |
4,787 | extension function should release the lock on entry and reacquire it on exit when resuming python code also note that even though the python code in python threads cannot truly overlap in time due to the gil synchronizationthe -coded portions of threads can any number may be running in parallelas long as they do work o... |
4,788 | exit explicitly with tools in the sys and os modules sys module exits for examplethe built-in sys exit function ends program when calledand earlier than normalsys exit(nexit with status nelse exits on end of script interestinglythis call really just raises the built-in systemexit exception because of thiswe can catch i... |
4,789 | print('ignored 'bye sys world ignored trylater(finallyprint('cleanup'bye sys world cleanup :\pp \system\exitsinteractive session process exits os module exits it' possible to exit python in other waystoo for instancewithin forked child process on unixwe typically call the os _exit function rather than sys exitthreads m... |
4,790 | tryoutahere(finallyprint('cleanup'bye os world ditto shell command exit status codes both the sys and os exit calls we just met accept an argument that denotes the exit status code of the process (it' optional in the sys call but required by osafter exitthis code may be interrogated in shells and by programs that ran t... |
4,791 | 'bye sys world\ stat pipe close(stat hex(stat' stat > returns exit code extract status from bitmask on unix-likes pipe os popen('python testexit_os py'stat pipe close(statstat > ( this code works the same under cygwin python on windows when using os popen on such unix-like platformsfor reasons we won' go into herethe e... |
4,792 | notice that the last test in the preceding code didn' attempt to read the command' output pipe if we dowe may have to run the target script in unbuffered mode with the - python command-line flag or change the script to flush its output manually with sys stdout flush otherwisethe text printed to the standard output stre... |
4,793 | call('python testexit_sys py'bye sys world pipe popen('python testexit_sys py'stdout=pipepipe communicate(( 'bye sys world\ \ 'nonepipe returncode the subprocess module works the same on unix-like platforms like cygwinbut unlike os popenthe exit status is not encodedand so it matches the windows result (note that shell... |
4,794 | os _exit(exitstatprint('never reached'def parent()while truenewpid os fork(start new copy of process if newpid = if in copyrun child logic child(loop until 'qconsole input elsepidstatus os wait(print('parent got'pidstatus(status > )if input(=' 'break if __name__ ='__main__'parent(running this program on linuxunixor cyg... |
4,795 | exitstat def child()global exitstat process global names exitstat + shared by all threads threadid thread get_ident(print('hello from child'threadidexitstatthread exit(print('never reached'def parent()while truethread start_new_thread(child()if input(=' 'break if __name__ ='__main__'parent(the following shows this scri... |
4,796 | process on windows!the alternative threading module for threads has no method equivalent to _thread exit()but since all that the latter does is raise system-exit exceptiondoing the same in threading has the same effect--the thread exits immediately and silentlyas in the following sort of code (see testexit-threading py... |
4,797 | simple files command-line arguments program exit status codes shell environment variables standard stream redirections stream pipes managed by os popen and subprocess for instancesending command-line options and writing to input streams lets us pass in program execution parametersreading program output streams and exit... |
4,798 | after this sectionwe'll also study the multiprocessing modulewhich offers additional and portable ipc options as part of its general process-launching apiincluding shared memoryand pipes and queues of arbitrary pickled python objects for nowlet' study traditional approaches first anonymous pipes pipesa cross-program co... |
4,799 | import ostime def child(pipeout)zzz while truetime sleep(zzzmsg ('spam % dzzzencode(os write(pipeoutmsgzzz (zzz+ make parent wait pipes are binary bytes send to parent goto after def parent()pipeinpipeout os pipe(make -ended pipe if os fork(= copy this process child(pipeoutin copyrun child elsein parentlisten to pipe w... |
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