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diff --git a/Doc/lib/libsubprocess.tex b/Doc/lib/libsubprocess.tex deleted file mode 100644 index e2a9bb6..0000000 --- a/Doc/lib/libsubprocess.tex +++ /dev/null @@ -1,340 +0,0 @@ -\section{\module{subprocess} --- Subprocess management} - -\declaremodule{standard}{subprocess} -\modulesynopsis{Subprocess management.} -\moduleauthor{Peter \AA strand}{astrand@lysator.liu.se} -\sectionauthor{Peter \AA strand}{astrand@lysator.liu.se} - -\versionadded{2.4} - -The \module{subprocess} module allows you to spawn new processes, -connect to their input/output/error pipes, and obtain their return -codes. This module intends to replace several other, older modules -and functions, such as: - -\begin{verbatim} -os.system -os.spawn* -commands.* -\end{verbatim} - -Information about how the \module{subprocess} module can be used to -replace these modules and functions can be found in the following -sections. - -\subsection{Using the subprocess Module} - -This module defines one class called \class{Popen}: - -\begin{classdesc}{Popen}{args, bufsize=0, executable=None, - stdin=None, stdout=None, stderr=None, - preexec_fn=None, close_fds=False, shell=False, - cwd=None, env=None, universal_newlines=False, - startupinfo=None, creationflags=0} - -Arguments are: - -\var{args} should be a string, or a sequence of program arguments. The -program to execute is normally the first item in the args sequence or -string, but can be explicitly set by using the executable argument. - -On \UNIX{}, with \var{shell=False} (default): In this case, the Popen -class uses \method{os.execvp()} to execute the child program. -\var{args} should normally be a sequence. A string will be treated as a -sequence with the string as the only item (the program to execute). - -On \UNIX{}, with \var{shell=True}: If args is a string, it specifies the -command string to execute through the shell. If \var{args} is a -sequence, the first item specifies the command string, and any -additional items will be treated as additional shell arguments. - -On Windows: the \class{Popen} class uses CreateProcess() to execute -the child program, which operates on strings. If \var{args} is a -sequence, it will be converted to a string using the -\method{list2cmdline} method. Please note that not all MS Windows -applications interpret the command line the same way: -\method{list2cmdline} is designed for applications using the same -rules as the MS C runtime. - -\var{bufsize}, if given, has the same meaning as the corresponding -argument to the built-in open() function: \constant{0} means unbuffered, -\constant{1} means line buffered, any other positive value means use a -buffer of (approximately) that size. A negative \var{bufsize} means to -use the system default, which usually means fully buffered. The default -value for \var{bufsize} is \constant{0} (unbuffered). - -The \var{executable} argument specifies the program to execute. It is -very seldom needed: Usually, the program to execute is defined by the -\var{args} argument. If \code{shell=True}, the \var{executable} -argument specifies which shell to use. On \UNIX{}, the default shell -is \file{/bin/sh}. On Windows, the default shell is specified by the -\envvar{COMSPEC} environment variable. - -\var{stdin}, \var{stdout} and \var{stderr} specify the executed -programs' standard input, standard output and standard error file -handles, respectively. Valid values are \code{PIPE}, an existing file -descriptor (a positive integer), an existing file object, and -\code{None}. \code{PIPE} indicates that a new pipe to the child -should be created. With \code{None}, no redirection will occur; the -child's file handles will be inherited from the parent. Additionally, -\var{stderr} can be \code{STDOUT}, which indicates that the stderr -data from the applications should be captured into the same file -handle as for stdout. - -If \var{preexec_fn} is set to a callable object, this object will be -called in the child process just before the child is executed. -(\UNIX{} only) - -If \var{close_fds} is true, all file descriptors except \constant{0}, -\constant{1} and \constant{2} will be closed before the child process is -executed. (\UNIX{} only). Or, on Windows, if \var{close_fds} is true -then no handles will be inherited by the child process. Note that on -Windows, you cannot set \var{close_fds} to true and also redirect the -standard handles by setting \var{stdin}, \var{stdout} or \var{stderr}. - -If \var{shell} is \constant{True}, the specified command will be -executed through the shell. - -If \var{cwd} is not \code{None}, the child's current directory will be -changed to \var{cwd} before it is executed. Note that this directory -is not considered when searching the executable, so you can't specify -the program's path relative to \var{cwd}. - -If \var{env} is not \code{None}, it defines the environment variables -for the new process. - -If \var{universal_newlines} is \constant{True}, the file objects stdout -and stderr are opened as text files, but lines may be terminated by -any of \code{'\e n'}, the \UNIX{} end-of-line convention, \code{'\e r'}, -the Macintosh convention or \code{'\e r\e n'}, the Windows convention. -All of these external representations are seen as \code{'\e n'} by the -Python program. \note{This feature is only available if Python is built -with universal newline support (the default). Also, the newlines -attribute of the file objects \member{stdout}, \member{stdin} and -\member{stderr} are not updated by the communicate() method.} - -The \var{startupinfo} and \var{creationflags}, if given, will be -passed to the underlying CreateProcess() function. They can specify -things such as appearance of the main window and priority for the new -process. (Windows only) -\end{classdesc} - -\subsubsection{Convenience Functions} - -This module also defines two shortcut functions: - -\begin{funcdesc}{call}{*popenargs, **kwargs} -Run command with arguments. Wait for command to complete, then -return the \member{returncode} attribute. - -The arguments are the same as for the Popen constructor. Example: - -\begin{verbatim} - retcode = call(["ls", "-l"]) -\end{verbatim} -\end{funcdesc} - -\begin{funcdesc}{check_call}{*popenargs, **kwargs} -Run command with arguments. Wait for command to complete. If the exit -code was zero then return, otherwise raise \exception{CalledProcessError.} -The \exception{CalledProcessError} object will have the return code in the -\member{returncode} attribute. - -The arguments are the same as for the Popen constructor. Example: - -\begin{verbatim} - check_call(["ls", "-l"]) -\end{verbatim} - -\versionadded{2.5} -\end{funcdesc} - -\subsubsection{Exceptions} - -Exceptions raised in the child process, before the new program has -started to execute, will be re-raised in the parent. Additionally, -the exception object will have one extra attribute called -\member{child_traceback}, which is a string containing traceback -information from the childs point of view. - -The most common exception raised is \exception{OSError}. This occurs, -for example, when trying to execute a non-existent file. Applications -should prepare for \exception{OSError} exceptions. - -A \exception{ValueError} will be raised if \class{Popen} is called -with invalid arguments. - -check_call() will raise \exception{CalledProcessError}, if the called -process returns a non-zero return code. - - -\subsubsection{Security} - -Unlike some other popen functions, this implementation will never call -/bin/sh implicitly. This means that all characters, including shell -metacharacters, can safely be passed to child processes. - - -\subsection{Popen Objects} - -Instances of the \class{Popen} class have the following methods: - -\begin{methoddesc}[Popen]{poll}{} -Check if child process has terminated. Returns returncode -attribute. -\end{methoddesc} - -\begin{methoddesc}[Popen]{wait}{} -Wait for child process to terminate. Returns returncode attribute. -\end{methoddesc} - -\begin{methoddesc}[Popen]{communicate}{input=None} -Interact with process: Send data to stdin. Read data from stdout and -stderr, until end-of-file is reached. Wait for process to terminate. -The optional \var{input} argument should be a string to be sent to the -child process, or \code{None}, if no data should be sent to the child. - -communicate() returns a tuple (stdout, stderr). - -\note{The data read is buffered in memory, so do not use this method -if the data size is large or unlimited.} -\end{methoddesc} - -The following attributes are also available: - -\begin{memberdesc}[Popen]{stdin} -If the \var{stdin} argument is \code{PIPE}, this attribute is a file -object that provides input to the child process. Otherwise, it is -\code{None}. -\end{memberdesc} - -\begin{memberdesc}[Popen]{stdout} -If the \var{stdout} argument is \code{PIPE}, this attribute is a file -object that provides output from the child process. Otherwise, it is -\code{None}. -\end{memberdesc} - -\begin{memberdesc}[Popen]{stderr} -If the \var{stderr} argument is \code{PIPE}, this attribute is file -object that provides error output from the child process. Otherwise, -it is \code{None}. -\end{memberdesc} - -\begin{memberdesc}[Popen]{pid} -The process ID of the child process. -\end{memberdesc} - -\begin{memberdesc}[Popen]{returncode} -The child return code. A \code{None} value indicates that the process -hasn't terminated yet. A negative value -N indicates that the child -was terminated by signal N (\UNIX{} only). -\end{memberdesc} - - -\subsection{Replacing Older Functions with the subprocess Module} - -In this section, "a ==> b" means that b can be used as a replacement -for a. - -\note{All functions in this section fail (more or less) silently if -the executed program cannot be found; this module raises an -\exception{OSError} exception.} - -In the following examples, we assume that the subprocess module is -imported with "from subprocess import *". - -\subsubsection{Replacing /bin/sh shell backquote} - -\begin{verbatim} -output=`mycmd myarg` -==> -output = Popen(["mycmd", "myarg"], stdout=PIPE).communicate()[0] -\end{verbatim} - -\subsubsection{Replacing shell pipe line} - -\begin{verbatim} -output=`dmesg | grep hda` -==> -p1 = Popen(["dmesg"], stdout=PIPE) -p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE) -output = p2.communicate()[0] -\end{verbatim} - -\subsubsection{Replacing os.system()} - -\begin{verbatim} -sts = os.system("mycmd" + " myarg") -==> -p = Popen("mycmd" + " myarg", shell=True) -sts = os.waitpid(p.pid, 0) -\end{verbatim} - -Notes: - -\begin{itemize} -\item Calling the program through the shell is usually not required. -\item It's easier to look at the \member{returncode} attribute than - the exit status. -\end{itemize} - -A more realistic example would look like this: - -\begin{verbatim} -try: - retcode = call("mycmd" + " myarg", shell=True) - if retcode < 0: - print >>sys.stderr, "Child was terminated by signal", -retcode - else: - print >>sys.stderr, "Child returned", retcode -except OSError as e: - print >>sys.stderr, "Execution failed:", e -\end{verbatim} - -\subsubsection{Replacing os.spawn*} - -P_NOWAIT example: - -\begin{verbatim} -pid = os.spawnlp(os.P_NOWAIT, "/bin/mycmd", "mycmd", "myarg") -==> -pid = Popen(["/bin/mycmd", "myarg"]).pid -\end{verbatim} - -P_WAIT example: - -\begin{verbatim} -retcode = os.spawnlp(os.P_WAIT, "/bin/mycmd", "mycmd", "myarg") -==> -retcode = call(["/bin/mycmd", "myarg"]) -\end{verbatim} - -Vector example: - -\begin{verbatim} -os.spawnvp(os.P_NOWAIT, path, args) -==> -Popen([path] + args[1:]) -\end{verbatim} - -Environment example: - -\begin{verbatim} -os.spawnlpe(os.P_NOWAIT, "/bin/mycmd", "mycmd", "myarg", env) -==> -Popen(["/bin/mycmd", "myarg"], env={"PATH": "/usr/bin"}) -\end{verbatim} - -\subsubsection{Replacing os.popen*} - -\begin{verbatim} -pipe = os.popen(cmd, mode='r', bufsize) -==> -pipe = Popen(cmd, shell=True, bufsize=bufsize, stdout=PIPE).stdout -\end{verbatim} - -\begin{verbatim} -pipe = os.popen(cmd, mode='w', bufsize) -==> -pipe = Popen(cmd, shell=True, bufsize=bufsize, stdin=PIPE).stdin -\end{verbatim} |