# HG changeset patch # Parent cca20d28f348c2cac3fe3d5fb3ca6d2a491410ca Issue #26240: Clean up the subprocess module doc string Patch by Tim Mitchell. diff -r cca20d28f348 Lib/subprocess.py --- a/Lib/subprocess.py Thu Oct 20 15:41:11 2016 -0400 +++ b/Lib/subprocess.py Sat Oct 22 00:54:29 2016 +0000 @@ -10,380 +10,24 @@ r"""subprocess - 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: +input/output/error pipes, and obtain their return codes. -os.system -os.spawn* -os.popen* -popen2.* -commands.* +For a complete description of this module see the Python documentation. -Information about how the subprocess module can be used to replace these -modules and functions can be found below. +Main 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 +Popen(...): A class for flexibly executing a command in a new process - - -Using the subprocess module -=========================== -This module defines one class called Popen: - -class 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: - -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 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 UNIX, 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, if given, has the same meaning as the corresponding argument -to the built-in open() function: 0 means unbuffered, 1 means line -buffered, any other positive value means use a buffer of -(approximately) that size. A negative bufsize means to use the system -default, which usually means fully buffered. The default value for -bufsize is 0 (unbuffered). - -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. - -If preexec_fn is set to a callable object, this object will be called -in the child process just before the child is executed. - -If close_fds is true, all file descriptors except 0, 1 and 2 will be -closed before the child process is executed. - -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. - -If env is not None, it defines the environment variables for the new -process. - -If universal_newlines is true, the file objects stdout and stderr are -opened as a text files, but lines may be terminated by any of '\n', -the Unix end-of-line convention, '\r', the Macintosh convention or -'\r\n', the Windows convention. All of these external representations -are seen as '\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 stdout, -stdin and stderr are not updated by the communicate() method. - -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 = 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: - - check_call(["ls", "-l"]) - -check_output(*popenargs, **kwargs): - Run command with arguments and return its output as a byte string. - - 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 = check_output(["ls", "-l", "/dev/null"]) - - -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. - -check_call() and check_output() will raise CalledProcessError, if the -called process returns a non-zero return code. - - -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 a string to be - sent to the child process, or 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. - -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 (UNIX 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 >>sys.stderr, "Child was terminated by signal", -retcode - else: - print >>sys.stderr, "Child returned", retcode -except OSError, e: - print >>sys.stderr, "Execution failed:", e - - -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"}) - - -Replacing os.popen* -------------------- -pipe = os.popen("cmd", mode='r', bufsize) -==> -pipe = Popen("cmd", shell=True, bufsize=bufsize, stdout=PIPE).stdout - -pipe = os.popen("cmd", mode='w', bufsize) -==> -pipe = Popen("cmd", shell=True, bufsize=bufsize, stdin=PIPE).stdin - - -(child_stdin, child_stdout) = os.popen2("cmd", mode, bufsize) -==> -p = Popen("cmd", shell=True, bufsize=bufsize, - stdin=PIPE, stdout=PIPE, close_fds=True) -(child_stdin, child_stdout) = (p.stdin, p.stdout) - - -(child_stdin, - child_stdout, - child_stderr) = os.popen3("cmd", mode, bufsize) -==> -p = Popen("cmd", shell=True, bufsize=bufsize, - stdin=PIPE, stdout=PIPE, stderr=PIPE, close_fds=True) -(child_stdin, - child_stdout, - child_stderr) = (p.stdin, p.stdout, p.stderr) - - -(child_stdin, child_stdout_and_stderr) = os.popen4("cmd", mode, - bufsize) -==> -p = Popen("cmd", shell=True, bufsize=bufsize, - stdin=PIPE, stdout=PIPE, stderr=STDOUT, close_fds=True) -(child_stdin, child_stdout_and_stderr) = (p.stdin, p.stdout) - -On Unix, os.popen2, os.popen3 and os.popen4 also accept a sequence as -the command to execute, in which case arguments will be passed -directly to the program without shell intervention. This usage can be -replaced as follows: - -(child_stdin, child_stdout) = os.popen2(["/bin/ls", "-l"], mode, - bufsize) -==> -p = Popen(["/bin/ls", "-l"], bufsize=bufsize, stdin=PIPE, stdout=PIPE) -(child_stdin, child_stdout) = (p.stdin, p.stdout) - -Return code handling translates as follows: - -pipe = os.popen("cmd", 'w') -... -rc = pipe.close() -if rc is not None and rc % 256: - print "There were some errors" -==> -process = Popen("cmd", 'w', shell=True, stdin=PIPE) -... -process.stdin.close() -if process.wait() != 0: - print "There were some errors" - - -Replacing popen2.* ------------------- -(child_stdout, child_stdin) = popen2.popen2("somestring", bufsize, mode) -==> -p = Popen(["somestring"], shell=True, bufsize=bufsize - stdin=PIPE, stdout=PIPE, close_fds=True) -(child_stdout, child_stdin) = (p.stdout, p.stdin) - -On Unix, popen2 also accepts a sequence as the command to execute, in -which case arguments will be passed directly to the program without -shell intervention. This usage can be replaced as follows: - -(child_stdout, child_stdin) = popen2.popen2(["mycmd", "myarg"], bufsize, - mode) -==> -p = Popen(["mycmd", "myarg"], bufsize=bufsize, - stdin=PIPE, stdout=PIPE, close_fds=True) -(child_stdout, child_stdin) = (p.stdout, p.stdin) - -The popen2.Popen3 and popen2.Popen4 basically works as subprocess.Popen, -except that: - -* subprocess.Popen raises an exception if the execution fails -* the capturestderr argument is replaced with the stderr argument. -* stdin=PIPE and stdout=PIPE must be specified. -* popen2 closes all filedescriptors by default, but you have to specify - close_fds=True with subprocess.Popen. +Constants +--------- +PIPE: Special value that indicates a pipe should be created +STDOUT: Special value that indicates that stderr should go to stdout """ import sys @@ -400,8 +44,9 @@ class CalledProcessError(Exception): """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. + + Attributes: + cmd, returncode, output """ def __init__(self, returncode, cmd, output=None): self.returncode = returncode @@ -646,6 +291,40 @@ 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) + + Attributes: + stdin, stdout, stderr, pid, returncode + """ _child_created = False # Set here since __del__ checks it def __init__(self, args, bufsize=0, executable=None, @@ -801,6 +480,8 @@ def poll(self): + """Check if child process has terminated. Set and return returncode + attribute.""" return self._internal_poll() diff -r cca20d28f348 Misc/ACKS --- a/Misc/ACKS Thu Oct 20 15:41:11 2016 -0400 +++ b/Misc/ACKS Sat Oct 22 00:54:29 2016 +0000 @@ -940,6 +940,7 @@ Andrii V. Mishkovskyi Dom Mitchell Dustin J. Mitchell +Tim Mitchell Zubin Mithra Florian Mladitsch Doug Moen