From 4afdca056b76143ac97d979b73cefa86fc1d654d Mon Sep 17 00:00:00 2001 From: Martin Panter Date: Tue, 25 Oct 2016 22:20:48 +0000 Subject: [PATCH] Issue #26240: Clean up the subprocess module doc string Patch by Tim Mitchell. --- Lib/subprocess.py | 427 +++++++++------------------------------------- Misc/ACKS | 1 + 2 files changed, 80 insertions(+), 348 deletions(-) diff --git a/Lib/subprocess.py b/Lib/subprocess.py index d8d6ab22747..502e26b9c42 100644 --- a/Lib/subprocess.py +++ b/Lib/subprocess.py @@ -7,352 +7,38 @@ # Licensed to PSF under a Contributor Agreement. # See http://www.python.org/2.4/license for licensing details. -r"""subprocess - Subprocesses with accessible I/O streams +r"""Subprocesses with accessible I/O streams This module allows you to spawn processes, connect to their -input/output/error pipes, and obtain their return codes. This module -intends to replace several older modules and functions: - -os.system -os.spawn* - -Information about how the subprocess module can be used to replace these -modules and functions can be found below. - - - -Using the subprocess module -=========================== -This module defines one class called Popen: - -class Popen(args, bufsize=-1, executable=None, - stdin=None, stdout=None, stderr=None, - preexec_fn=None, close_fds=True, shell=False, - cwd=None, env=None, universal_newlines=False, - startupinfo=None, creationflags=0, - restore_signals=True, start_new_session=False, pass_fds=()): - - -Arguments are: - -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 POSIX, with shell=False (default): In this case, the Popen class -uses os.execvp() to execute the child program. 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 POSIX, with shell=True: If args is a string, it specifies the -command string to execute through the shell. If 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 Popen class uses CreateProcess() to execute the child -program, which operates on strings. If args is a sequence, it will be -converted to a string using the list2cmdline method. Please note that -not all MS Windows applications interpret the command line the same -way: The list2cmdline is designed for applications using the same -rules as the MS C runtime. - -bufsize will be supplied as the corresponding argument to the io.open() -function when creating the stdin/stdout/stderr pipe file objects: -0 means unbuffered (read & write are one system call and can return short), -1 means line buffered, any other positive value means use a buffer of -approximately that size. A negative bufsize, the default, means the system -default of io.DEFAULT_BUFFER_SIZE will be used. - -stdin, stdout and stderr specify the executed programs' standard -input, standard output and standard error file handles, respectively. -Valid values are PIPE, an existing file descriptor (a positive -integer), an existing file object, and None. PIPE indicates that a -new pipe to the child should be created. With None, no redirection -will occur; the child's file handles will be inherited from the -parent. Additionally, stderr can be STDOUT, which indicates that the -stderr data from the applications should be captured into the same -file handle as for stdout. - -On POSIX, if preexec_fn is set to a callable object, this object will be -called in the child process just before the child is executed. The use -of preexec_fn is not thread safe, using it in the presence of threads -could lead to a deadlock in the child process before the new executable -is executed. - -If close_fds is true, all file descriptors except 0, 1 and 2 will be -closed before the child process is executed. The default for close_fds -varies by platform: Always true on POSIX. True when stdin/stdout/stderr -are None on Windows, false otherwise. - -pass_fds is an optional sequence of file descriptors to keep open between the -parent and child. Providing any pass_fds implicitly sets close_fds to true. - -if shell is true, the specified command will be executed through the -shell. - -If cwd is not None, the current directory will be changed to cwd -before the child is executed. - -On POSIX, if restore_signals is True all signals that Python sets to -SIG_IGN are restored to SIG_DFL in the child process before the exec. -Currently this includes the SIGPIPE, SIGXFZ and SIGXFSZ signals. This -parameter does nothing on Windows. - -On POSIX, if start_new_session is True, the setsid() system call will be made -in the child process prior to executing the command. - -If env is not None, it defines the environment variables for the new -process. - -If universal_newlines is False, the file objects stdin, stdout and stderr -are opened as binary files, and no line ending conversion is done. - -If universal_newlines is True, the file objects stdout and stderr are -opened as a text file, but lines may be terminated by any of '\n', -the Unix end-of-line convention, '\r', the old Macintosh convention or -'\r\n', the Windows convention. All of these external representations -are seen as '\n' by the Python program. Also, the newlines attribute -of the file objects stdout, stdin and stderr are not updated by the -communicate() method. - -In either case, the process being communicated with should start up -expecting to receive bytes on its standard input and decode them with -the same encoding they are sent in. - -The startupinfo and 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) - - -This module also defines some shortcut functions: - -call(*popenargs, **kwargs): - Run command with arguments. Wait for command to complete, then - return the returncode attribute. - - The arguments are the same as for the Popen constructor. Example: - - >>> retcode = subprocess.call(["ls", "-l"]) - -check_call(*popenargs, **kwargs): - Run command with arguments. Wait for command to complete. If the - exit code was zero then return, otherwise raise - CalledProcessError. The CalledProcessError object will have the - return code in the returncode attribute. - - The arguments are the same as for the Popen constructor. Example: - - >>> subprocess.check_call(["ls", "-l"]) - 0 - -getstatusoutput(cmd): - Return (status, output) of executing cmd in a shell. - - Execute the string 'cmd' in a shell with 'check_output' and - return a 2-tuple (status, output). Universal newlines mode is used, - meaning that the result with be decoded to a string. - - A trailing newline is stripped from the output. - The exit status for the command can be interpreted - according to the rules for the function 'wait'. Example: - - >>> subprocess.getstatusoutput('ls /bin/ls') - (0, '/bin/ls') - >>> subprocess.getstatusoutput('cat /bin/junk') - (256, 'cat: /bin/junk: No such file or directory') - >>> subprocess.getstatusoutput('/bin/junk') - (256, 'sh: /bin/junk: not found') - -getoutput(cmd): - Return output (stdout or stderr) of executing cmd in a shell. - - Like getstatusoutput(), except the exit status is ignored and the return - value is a string containing the command's output. Example: - - >>> subprocess.getoutput('ls /bin/ls') - '/bin/ls' - -check_output(*popenargs, **kwargs): - Run command with arguments and return its output. - - If the exit code was non-zero it raises a CalledProcessError. The - CalledProcessError object will have the return code in the returncode - attribute and output in the output attribute. - - The arguments are the same as for the Popen constructor. Example: - - >>> output = subprocess.check_output(["ls", "-l", "/dev/null"]) - - There is an additional optional argument, "input", allowing you to - pass a string to the subprocess's stdin. If you use this argument - you may not also use the Popen constructor's "stdin" argument. - - If universal_newlines is set to True, the "input" argument must - be a string rather than bytes, and the return value will be a string. - -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 -'child_traceback', which is a string containing traceback information -from the child's point of view. - -The most common exception raised is OSError. This occurs, for -example, when trying to execute a non-existent file. Applications -should prepare for OSErrors. - -A ValueError will be raised if Popen is called with invalid arguments. - -Exceptions defined within this module inherit from SubprocessError. -check_call() and check_output() will raise CalledProcessError if the -called process returns a non-zero return code. TimeoutExpired -be raised if a timeout was specified and expired. - - -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. - - -Popen objects -============= -Instances of the Popen class have the following methods: - -poll() - Check if child process has terminated. Returns returncode - attribute. - -wait() - Wait for child process to terminate. Returns returncode attribute. - -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 input argument should be data to be - sent to the child process, or None, if no data should be sent to - the child. If the Popen instance was constructed with universal_newlines - set to True, the input argument should be a string and will be encoded - using the preferred system encoding (see locale.getpreferredencoding); - if universal_newlines is False, the input argument should be a - byte string. - - 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. - -The following attributes are also available: - -stdin - If the stdin argument is PIPE, this attribute is a file object - that provides input to the child process. Otherwise, it is None. - -stdout - If the stdout argument is PIPE, this attribute is a file object - that provides output from the child process. Otherwise, it is - None. - -stderr - If the stderr argument is PIPE, this attribute is file object that - provides error output from the child process. Otherwise, it is - None. - -pid - The process ID of the child process. - -returncode - The child return code. A None value indicates that the process - hasn't terminated yet. A negative value -N indicates that the - child was terminated by signal N (POSIX only). - - -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 OSError -exception. - -In the following examples, we assume that the subprocess module is -imported with "from subprocess import *". - - -Replacing /bin/sh shell backquote ---------------------------------- -output=`mycmd myarg` -==> -output = Popen(["mycmd", "myarg"], stdout=PIPE).communicate()[0] - - -Replacing shell pipe line -------------------------- -output=`dmesg | grep hda` -==> -p1 = Popen(["dmesg"], stdout=PIPE) -p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE) -output = p2.communicate()[0] - - -Replacing os.system() ---------------------- -sts = os.system("mycmd" + " myarg") -==> -p = Popen("mycmd" + " myarg", shell=True) -pid, sts = os.waitpid(p.pid, 0) - -Note: - -* Calling the program through the shell is usually not required. - -* It's easier to look at the returncode attribute than the - exitstatus. - -A more real-world example would look like this: - -try: - retcode = call("mycmd" + " myarg", shell=True) - if retcode < 0: - print("Child was terminated by signal", -retcode, file=sys.stderr) - else: - print("Child returned", retcode, file=sys.stderr) -except OSError as e: - print("Execution failed:", e, file=sys.stderr) - - -Replacing os.spawn* -------------------- -P_NOWAIT example: - -pid = os.spawnlp(os.P_NOWAIT, "/bin/mycmd", "mycmd", "myarg") -==> -pid = Popen(["/bin/mycmd", "myarg"]).pid - - -P_WAIT example: - -retcode = os.spawnlp(os.P_WAIT, "/bin/mycmd", "mycmd", "myarg") -==> -retcode = call(["/bin/mycmd", "myarg"]) - - -Vector example: - -os.spawnvp(os.P_NOWAIT, path, args) -==> -Popen([path] + args[1:]) - - -Environment example: - -os.spawnlpe(os.P_NOWAIT, "/bin/mycmd", "mycmd", "myarg", env) -==> -Popen(["/bin/mycmd", "myarg"], env={"PATH": "/usr/bin"}) +input/output/error pipes, and obtain their return codes. + +For a complete description of this module see the Python documentation. + +Main API +======== +run(...): Runs a command, waits for it to complete, then returns a + CompletedProcess instance. +Popen(...): A class for flexibly executing a command in a new process + +Constants +--------- +DEVNULL: Special value that indicates that os.devnull should be used +PIPE: Special value that indicates a pipe should be created +STDOUT: Special value that indicates that stderr should go to stdout + + +Older API +========= +call(...): Runs a command, waits for it to complete, then returns + the return code. +check_call(...): Same as call() but raises CalledProcessError() + if return code is not 0 +check_output(...): Same as check_call() but returns the contents of + stdout instead of a return code +getoutput(...): Runs a command in the shell, waits for it to complete, + then returns the output +getstatusoutput(...): Runs a command in the shell, waits for it to complete, + then returns a (status, output) tuple """ import sys @@ -372,10 +58,11 @@ class SubprocessError(Exception): pass class CalledProcessError(SubprocessError): - """This exception is raised when a process run by check_call() or - check_output() returns a non-zero exit status. - The exit status will be stored in the returncode attribute; - check_output() will also store the output in the output attribute. + """Raised when run() is called with check=True and the process + returns a non-zero exit status. + + Attributes: + cmd, returncode, stdout, stderr, output """ def __init__(self, returncode, cmd, output=None, stderr=None): self.returncode = returncode @@ -401,6 +88,9 @@ class CalledProcessError(SubprocessError): class TimeoutExpired(SubprocessError): """This exception is raised when the timeout expires while waiting for a child process. + + Attributes: + cmd, output, stdout, stderr, timeout """ def __init__(self, cmd, timeout, output=None, stderr=None): self.cmd = cmd @@ -828,7 +518,46 @@ _PLATFORM_DEFAULT_CLOSE_FDS = object() class Popen(object): + """ Execute a child program in a new process. + For a complete description of the arguments see the Python documentation. + + Arguments: + args: A string, or a sequence of program arguments. + + bufsize: supplied as the buffering argument to the open() function when + creating the stdin/stdout/stderr pipe file objects + + executable: A replacement program to execute. + + stdin, stdout and stderr: These specify the executed programs' standard + input, standard output and standard error file handles, respectively. + + preexec_fn: (POSIX only) An object to be called in the child process + just before the child is executed. + + close_fds: Controls closing or inheriting of file descriptors. + + shell: If true, the command will be executed through the shell. + + cwd: Sets the current directory before the child is executed. + + env: Defines the environment variables for the new process. + + universal_newlines: If true, use universal line endings for file + objects stdin, stdout and stderr. + + startupinfo and creationflags (Windows only) + + restore_signals (POSIX only) + + start_new_session (POSIX only) + + pass_fds (POSIX only) + + Attributes: + stdin, stdout, stderr, pid, returncode + """ _child_created = False # Set here since __del__ checks it def __init__(self, args, bufsize=-1, executable=None, @@ -1079,6 +808,8 @@ class Popen(object): def poll(self): + """Check if child process has terminated. Set and return returncode + attribute.""" return self._internal_poll() diff --git a/Misc/ACKS b/Misc/ACKS index 8c5c0c203ff..2ba9ea14cc7 100644 --- a/Misc/ACKS +++ b/Misc/ACKS @@ -999,6 +999,7 @@ Julien Miotte Andrii V. Mishkovskyi Dom Mitchell Dustin J. Mitchell +Tim Mitchell Zubin Mithra Florian Mladitsch Doug Moen