# subprocess - Subprocesses with accessible I/O streams

#

# For more information about this module, see PEP 324.

#

# This module should remain compatible with Python 2.2, see PEP 291.

#

# Copyright (c) 2003-2005 by Peter Astrand <astrand@lysator.liu.se>

#

# 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



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 other, older modules and functions, like:



os.system

os.spawn*

os.popen*

popen2.*

commands.*



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=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 two 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"])



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 childs 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() 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 != 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.

"""



import sys

mswindows = (sys.platform == "win32")



import os

import types

import traceback

import gc

import signal



# Exception classes used by this module.

class CalledProcessError(Exception):

    """This exception is raised when a process run by check_call() returns

    a non-zero exit status.  The exit status will be stored in the

    returncode attribute."""

    def __init__(self, returncode, cmd):

        self.returncode = returncode

        self.cmd = cmd

    def __str__(self):

        return "Command '%s' returned non-zero exit status %d" % (self.cmd, self.returncode)





if mswindows:

    import threading

    import msvcrt

    if 0: # <-- change this to use pywin32 instead of the _subprocess driver

        import pywintypes

        from win32api import GetStdHandle, STD_INPUT_HANDLE, \

                             STD_OUTPUT_HANDLE, STD_ERROR_HANDLE

        from win32api import GetCurrentProcess, DuplicateHandle, \

                             GetModuleFileName, GetVersion

        from win32con import DUPLICATE_SAME_ACCESS, SW_HIDE

        from win32pipe import CreatePipe

        from win32process import CreateProcess, STARTUPINFO, \

                                 GetExitCodeProcess, STARTF_USESTDHANDLES, \

                                 STARTF_USESHOWWINDOW, CREATE_NEW_CONSOLE

        from win32process import TerminateProcess

        from win32event import WaitForSingleObject, INFINITE, WAIT_OBJECT_0

    else:

        from _subprocess import *

        class STARTUPINFO:

            dwFlags = 0

            hStdInput = None

            hStdOutput = None

            hStdError = None

            wShowWindow = 0

        class pywintypes:

            error = IOError

else:

    import select

    import errno

    import fcntl

    import pickle



__all__ = ["Popen", "PIPE", "STDOUT", "call", "check_call", "CalledProcessError"]



try:

    MAXFD = os.sysconf("SC_OPEN_MAX")

except:

    MAXFD = 256



# True/False does not exist on 2.2.0

#try:

#    False

#except NameError:

#    False = 0

#    True = 1



_active = []



def _cleanup():

    for inst in _active[:]:

        if inst._internal_poll(_deadstate=sys.maxint) >= 0:

            try:

                _active.remove(inst)

            except ValueError:

                # This can happen if two threads create a new Popen instance.

                # It's harmless that it was already removed, so ignore.

                pass



PIPE = -1

STDOUT = -2





def 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"])

    """

    return Popen(*popenargs, **kwargs).wait()





def 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"])

    """

    retcode = call(*popenargs, **kwargs)

    cmd = kwargs.get("args")

    if cmd is None:

        cmd = popenargs[0]

    if retcode:

        raise CalledProcessError(retcode, cmd)

    return retcode





def list2cmdline(seq):

    """

    Translate a sequence of arguments into a command line

    string, using the same rules as the MS C runtime:



    1) Arguments are delimited by white space, which is either a

       space or a tab.



    2) A string surrounded by double quotation marks is

       interpreted as a single argument, regardless of white space

       or pipe characters contained within.  A quoted string can be

       embedded in an argument.



    3) A double quotation mark preceded by a backslash is

       interpreted as a literal double quotation mark.



    4) Backslashes are interpreted literally, unless they

       immediately precede a double quotation mark.



    5) If backslashes immediately precede a double quotation mark,

       every pair of backslashes is interpreted as a literal

       backslash.  If the number of backslashes is odd, the last

       backslash escapes the next double quotation mark as

       described in rule 3.

    """



    # See

    # http://msdn.microsoft.com/library/en-us/vccelng/htm/progs_12.asp

    result = []

    needquote = False

    for arg in seq:

        bs_buf = []



        # Add a space to separate this argument from the others

        if result:

            result.append(' ')



        needquote = (" " in arg) or ("\t" in arg) or ("|" in arg) or not arg

        if needquote:

            result.append('"')



        for c in arg:

            if c == '\\':

                # Don't know if we need to double yet.

                bs_buf.append(c)

            elif c == '"':

                # Double backslashes.

                result.append('\\' * len(bs_buf)*2)

                bs_buf = []

                result.append('\\"')

            else:

                # Normal char

                if bs_buf:

                    result.extend(bs_buf)

                    bs_buf = []

                result.append(c)



        # Add remaining backslashes, if any.

        if bs_buf:

            result.extend(bs_buf)



        if needquote:

            result.extend(bs_buf)

            result.append('"')



    return ''.join(result)





class Popen(object):

    def __init__(self, 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):

        """Create new Popen instance."""

        _cleanup()



        self._child_created = False

        if not isinstance(bufsize, (int, long)):

            raise TypeError("bufsize must be an integer")



        if mswindows:

            if preexec_fn is not None:

                raise ValueError("preexec_fn is not supported on Windows "

                                 "platforms")

            if close_fds and (stdin is not None or stdout is not None or

                              stderr is not None):

                raise ValueError("close_fds is not supported on Windows "

                                 "platforms if you redirect stdin/stdout/stderr")

        else:

            # POSIX

            if startupinfo is not None:

                raise ValueError("startupinfo is only supported on Windows "

                                 "platforms")

            if creationflags != 0:

                raise ValueError("creationflags is only supported on Windows "

                                 "platforms")



        self.stdin = None

        self.stdout = None

        self.stderr = None

        self.pid = None

        self.returncode = None

        self.universal_newlines = universal_newlines



        # Input and output objects. The general principle is like

        # this:

        #

        # Parent                   Child

        # ------                   -----

        # p2cwrite   ---stdin--->  p2cread

        # c2pread    <--stdout---  c2pwrite

        # errread    <--stderr---  errwrite

        #

        # On POSIX, the child objects are file descriptors.  On

        # Windows, these are Windows file handles.  The parent objects

        # are file descriptors on both platforms.  The parent objects

        # are None when not using PIPEs. The child objects are None

        # when not redirecting.



        (p2cread, p2cwrite,

         c2pread, c2pwrite,

         errread, errwrite) = self._get_handles(stdin, stdout, stderr)



        self._execute_child(args, executable, preexec_fn, close_fds,

                            cwd, env, universal_newlines,

                            startupinfo, creationflags, shell,

                            p2cread, p2cwrite,

                            c2pread, c2pwrite,

                            errread, errwrite)



        if mswindows:

            if p2cwrite is not None:

                p2cwrite = msvcrt.open_osfhandle(p2cwrite.Detach(), 0)

            if c2pread is not None:

                c2pread = msvcrt.open_osfhandle(c2pread.Detach(), 0)

            if errread is not None:

                errread = msvcrt.open_osfhandle(errread.Detach(), 0)



        if p2cwrite is not None:

            self.stdin = os.fdopen(p2cwrite, 'wb', bufsize)

        if c2pread is not None:

            if universal_newlines:

                self.stdout = os.fdopen(c2pread, 'rU', bufsize)

            else:

                self.stdout = os.fdopen(c2pread, 'rb', bufsize)

        if errread is not None:

            if universal_newlines:

                self.stderr = os.fdopen(errread, 'rU', bufsize)

            else:

                self.stderr = os.fdopen(errread, 'rb', bufsize)





    def _translate_newlines(self, data):

        data = data.replace("\r\n", "\n")

        data = data.replace("\r", "\n")

        return data





    def __del__(self, sys=sys):

        if not self._child_created:

            # We didn't get to successfully create a child process.

            return

        # In case the child hasn't been waited on, check if it's done.

        self._internal_poll(_deadstate=sys.maxint)

        if self.returncode is None and _active is not None:

            # Child is still running, keep us alive until we can wait on it.

            _active.append(self)





    def communicate(self, 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)."""



        # Optimization: If we are only using one pipe, or no pipe at

        # all, using select() or threads is unnecessary.

        if [self.stdin, self.stdout, self.stderr].count(None) >= 2:

            stdout = None

            stderr = None

            if self.stdin:

                if input:

                    self.stdin.write(input)

                self.stdin.close()

            elif self.stdout:

                stdout = self.stdout.read()

                self.stdout.close()

            elif self.stderr:

                stderr = self.stderr.read()

                self.stderr.close()

            self.wait()

            return (stdout, stderr)



        return self._communicate(input)





    def poll(self):

        return self._internal_poll()





    if mswindows:

        #

        # Windows methods

        #

        def _get_handles(self, stdin, stdout, stderr):

            """Construct and return tupel with IO objects:

            p2cread, p2cwrite, c2pread, c2pwrite, errread, errwrite

            """

            if stdin is None and stdout is None and stderr is None:

                return (None, None, None, None, None, None)



            p2cread, p2cwrite = None, None

            c2pread, c2pwrite = None, None

            errread, errwrite = None, None



            if stdin is None:

                p2cread = GetStdHandle(STD_INPUT_HANDLE)

                if p2cread is None:

                    p2cread, _ = CreatePipe(None, 0)

            elif stdin == PIPE:

                p2cread, p2cwrite = CreatePipe(None, 0)

            elif isinstance(stdin, int):

                p2cread = msvcrt.get_osfhandle(stdin)

            else:

                # Assuming file-like object

                p2cread = msvcrt.get_osfhandle(stdin.fileno())

            p2cread = self._make_inheritable(p2cread)



            if stdout is None:

                c2pwrite = GetStdHandle(STD_OUTPUT_HANDLE)

                if c2pwrite is None:

                    _, c2pwrite = CreatePipe(None, 0)

            elif stdout == PIPE:

                c2pread, c2pwrite = CreatePipe(None, 0)

            elif isinstance(stdout, int):

                c2pwrite = msvcrt.get_osfhandle(stdout)

            else:

                # Assuming file-like object

                c2pwrite = msvcrt.get_osfhandle(stdout.fileno())

            c2pwrite = self._make_inheritable(c2pwrite)



            if stderr is None:

                errwrite = GetStdHandle(STD_ERROR_HANDLE)

                if errwrite is None:

                    _, errwrite = CreatePipe(None, 0)

            elif stderr == PIPE:

                errread, errwrite = CreatePipe(None, 0)

            elif stderr == STDOUT:

                errwrite = c2pwrite

            elif isinstance(stderr, int):

                errwrite = msvcrt.get_osfhandle(stderr)

            else:

                # Assuming file-like object

                errwrite = msvcrt.get_osfhandle(stderr.fileno())

            errwrite = self._make_inheritable(errwrite)



            return (p2cread, p2cwrite,

                    c2pread, c2pwrite,

                    errread, errwrite)





        def _make_inheritable(self, handle):

            """Return a duplicate of handle, which is inheritable"""

            return DuplicateHandle(GetCurrentProcess(), handle,

                                   GetCurrentProcess(), 0, 1,

                                   DUPLICATE_SAME_ACCESS)





        def _find_w9xpopen(self):

            """Find and return absolut path to w9xpopen.exe"""

            w9xpopen = os.path.join(os.path.dirname(GetModuleFileName(0)),

                                    "w9xpopen.exe")

            if not os.path.exists(w9xpopen):

                # Eeek - file-not-found - possibly an embedding

                # situation - see if we can locate it in sys.exec_prefix

                w9xpopen = os.path.join(os.path.dirname(sys.exec_prefix),

                                        "w9xpopen.exe")

                if not os.path.exists(w9xpopen):

                    raise RuntimeError("Cannot locate w9xpopen.exe, which is "

                                       "needed for Popen to work with your "

                                       "shell or platform.")

            return w9xpopen





        def _execute_child(self, args, executable, preexec_fn, close_fds,

                           cwd, env, universal_newlines,

                           startupinfo, creationflags, shell,

                           p2cread, p2cwrite,

                           c2pread, c2pwrite,

                           errread, errwrite):

            """Execute program (MS Windows version)"""



            if not isinstance(args, types.StringTypes):

                args = list2cmdline(args)



            # Process startup details

            if startupinfo is None:

                startupinfo = STARTUPINFO()

            if None not in (p2cread, c2pwrite, errwrite):

                startupinfo.dwFlags |= STARTF_USESTDHANDLES

                startupinfo.hStdInput = p2cread

                startupinfo.hStdOutput = c2pwrite

                startupinfo.hStdError = errwrite



            if shell:

                startupinfo.dwFlags |= STARTF_USESHOWWINDOW

                startupinfo.wShowWindow = SW_HIDE

                comspec = os.environ.get("COMSPEC", "cmd.exe")

                args = comspec + " /c " + args

                if (GetVersion() >= 0x80000000L or

                        os.path.basename(comspec).lower() == "command.com"):

                    # Win9x, or using command.com on NT. We need to

                    # use the w9xpopen intermediate program. For more

                    # information, see KB Q150956

                    # (http://web.archive.org/web/20011105084002/http://support.microsoft.com/support/kb/articles/Q150/9/56.asp)

                    w9xpopen = self._find_w9xpopen()

                    args = '"%s" %s' % (w9xpopen, args)

                    # Not passing CREATE_NEW_CONSOLE has been known to

                    # cause random failures on win9x.  Specifically a

                    # dialog: "Your program accessed mem currently in

                    # use at xxx" and a hopeful warning about the

                    # stability of your system.  Cost is Ctrl+C wont

                    # kill children.

                    creationflags |= CREATE_NEW_CONSOLE



            # Start the process

            try:

                hp, ht, pid, tid = CreateProcess(executable, args,

                                         # no special security

                                         None, None,

                                         int(not close_fds),

                                         creationflags,

                                         env,

                                         cwd,

                                         startupinfo)

            except pywintypes.error, e:

                # Translate pywintypes.error to WindowsError, which is

                # a subclass of OSError.  FIXME: We should really

                # translate errno using _sys_errlist (or simliar), but

                # how can this be done from Python?

                raise WindowsError(*e.args)



            # Retain the process handle, but close the thread handle

            self._child_created = True

            self._handle = hp

            self.pid = pid

            ht.Close()



            # Child is launched. Close the parent's copy of those pipe

            # handles that only the child should have open.  You need

            # to make sure that no handles to the write end of the

            # output pipe are maintained in this process or else the

            # pipe will not close when the child process exits and the

            # ReadFile will hang.

            if p2cread is not None:

                p2cread.Close()

            if c2pwrite is not None:

                c2pwrite.Close()

            if errwrite is not None:

                errwrite.Close()





        def _internal_poll(self, _deadstate=None):

            """Check if child process has terminated.  Returns returncode

            attribute."""

            if self.returncode is None:

                if WaitForSingleObject(self._handle, 0) == WAIT_OBJECT_0:

                    self.returncode = GetExitCodeProcess(self._handle)

            return self.returncode





        def wait(self):

            """Wait for child process to terminate.  Returns returncode

            attribute."""

            if self.returncode is None:

                obj = WaitForSingleObject(self._handle, INFINITE)

                self.returncode = GetExitCodeProcess(self._handle)

            return self.returncode





        def _readerthread(self, fh, buffer):

            buffer.append(fh.read())





        def _communicate(self, input):

            stdout = None # Return

            stderr = None # Return



            if self.stdout:

                stdout = []

                stdout_thread = threading.Thread(target=self._readerthread,

                                                 args=(self.stdout, stdout))

                stdout_thread.setDaemon(True)

                stdout_thread.start()

            if self.stderr:

                stderr = []

                stderr_thread = threading.Thread(target=self._readerthread,

                                                 args=(self.stderr, stderr))

                stderr_thread.setDaemon(True)

                stderr_thread.start()



            if self.stdin:

                if input is not None:

                    self.stdin.write(input)

                self.stdin.close()



            if self.stdout:

                stdout_thread.join()

            if self.stderr:

                stderr_thread.join()



            # All data exchanged.  Translate lists into strings.

            if stdout is not None:

                stdout = stdout[0]

            if stderr is not None:

                stderr = stderr[0]



            # Translate newlines, if requested.  We cannot let the file

            # object do the translation: It is based on stdio, which is

            # impossible to combine with select (unless forcing no

            # buffering).

            if self.universal_newlines and hasattr(file, 'newlines'):

                if stdout:

                    stdout = self._translate_newlines(stdout)

                if stderr:

                    stderr = self._translate_newlines(stderr)



            self.wait()

            return (stdout, stderr)



        def send_signal(self, sig):

            """Send a signal to the process

            """

            if sig == signal.SIGTERM:

                self.terminate()

            else:

                raise ValueError("Only SIGTERM is supported on Windows")



        def terminate(self):

            """Terminates the process

            """

            TerminateProcess(self._handle, 1)



        kill = terminate



    else:

        #

        # POSIX methods

        #

        def _get_handles(self, stdin, stdout, stderr):

            """Construct and return tupel with IO objects:

            p2cread, p2cwrite, c2pread, c2pwrite, errread, errwrite

            """

            p2cread, p2cwrite = None, None

            c2pread, c2pwrite = None, None

            errread, errwrite = None, None



            if stdin is None:

                pass

            elif stdin == PIPE:

                p2cread, p2cwrite = os.pipe()

            elif isinstance(stdin, int):

                p2cread = stdin

            else:

                # Assuming file-like object

                p2cread = stdin.fileno()



            if stdout is None:

                pass

            elif stdout == PIPE:

                c2pread, c2pwrite = os.pipe()

            elif isinstance(stdout, int):

                c2pwrite = stdout

            else:

                # Assuming file-like object

                c2pwrite = stdout.fileno()



            if stderr is None:

                pass

            elif stderr == PIPE:

                errread, errwrite = os.pipe()

            elif stderr == STDOUT:

                errwrite = c2pwrite

            elif isinstance(stderr, int):

                errwrite = stderr

            else:

                # Assuming file-like object

                errwrite = stderr.fileno()



            return (p2cread, p2cwrite,

                    c2pread, c2pwrite,

                    errread, errwrite)





        def _set_cloexec_flag(self, fd):

            try:

                cloexec_flag = fcntl.FD_CLOEXEC

            except AttributeError:

                cloexec_flag = 1



            old = fcntl.fcntl(fd, fcntl.F_GETFD)

            fcntl.fcntl(fd, fcntl.F_SETFD, old | cloexec_flag)





        def _close_fds(self, but):

            os.closerange(3, but)

            os.closerange(but + 1, MAXFD)





        def _execute_child(self, args, executable, preexec_fn, close_fds,

                           cwd, env, universal_newlines,

                           startupinfo, creationflags, shell,

                           p2cread, p2cwrite,

                           c2pread, c2pwrite,

                           errread, errwrite):

            """Execute program (POSIX version)"""



            if isinstance(args, types.StringTypes):

                args = [args]

            else:

                args = list(args)



            if shell:

                args = ["/bin/sh", "-c"] + args



            if executable is None:

                executable = args[0]



            # For transferring possible exec failure from child to parent

            # The first char specifies the exception type: 0 means

            # OSError, 1 means some other error.

            errpipe_read, errpipe_write = os.pipe()

            try:

                try:

                    self._set_cloexec_flag(errpipe_write)



                    gc_was_enabled = gc.isenabled()

                    # Disable gc to avoid bug where gc -> file_dealloc ->

                    # write to stderr -> hang.  http://bugs.python.org/issue1336

                    gc.disable()

                    try:

                        self.pid = os.fork()

                    except:

                        if gc_was_enabled:

                            gc.enable()

                        raise

                    self._child_created = True

                    if self.pid == 0:

                        # Child

                        try:

                            # Close parent's pipe ends

                            if p2cwrite is not None:

                                os.close(p2cwrite)

                            if c2pread is not None:

                                os.close(c2pread)

                            if errread is not None:

                                os.close(errread)

                            os.close(errpipe_read)



                            # Dup fds for child

                            if p2cread is not None:

                                os.dup2(p2cread, 0)

                            if c2pwrite is not None:

                                os.dup2(c2pwrite, 1)

                            if errwrite is not None:

                                os.dup2(errwrite, 2)



                            # Close pipe fds.  Make sure we don't close the same

                            # fd more than once, or standard fds.

                            if p2cread is not None and p2cread not in (0,):

                                os.close(p2cread)

                            if c2pwrite is not None and c2pwrite not in (p2cread, 1):

                                os.close(c2pwrite)

                            if errwrite is not None and errwrite not in (p2cread, c2pwrite, 2):

                                os.close(errwrite)



                            # Close all other fds, if asked for

                            if close_fds:

                                self._close_fds(but=errpipe_write)



                            if cwd is not None:

                                os.chdir(cwd)



                            if preexec_fn:

                                preexec_fn()



                            if env is None:

                                os.execvp(executable, args)

                            else:

                                os.execvpe(executable, args, env)



                        except:

                            exc_type, exc_value, tb = sys.exc_info()

                            # Save the traceback and attach it to the exception object

                            exc_lines = traceback.format_exception(exc_type,

                                                                   exc_value,

                                                                   tb)

                            exc_value.child_traceback = ''.join(exc_lines)

                            os.write(errpipe_write, pickle.dumps(exc_value))



                        # This exitcode won't be reported to applications, so it

                        # really doesn't matter what we return.

                        os._exit(255)



                    # Parent

                    if gc_was_enabled:

                        gc.enable()

                finally:

                    # be sure the FD is closed no matter what

                    os.close(errpipe_write)



                if p2cread is not None and p2cwrite is not None:

                    os.close(p2cread)

                if c2pwrite is not None and c2pread is not None:

                    os.close(c2pwrite)

                if errwrite is not None and errread is not None:

                    os.close(errwrite)



                # Wait for exec to fail or succeed; possibly raising exception

                data = os.read(errpipe_read, 1048576) # Exceptions limited to 1 MB

            finally:

                # be sure the FD is closed no matter what

                os.close(errpipe_read)



            if data != "":

                os.waitpid(self.pid, 0)

                child_exception = pickle.loads(data)

                for fd in (p2cwrite, c2pread, errread):

                    if fd is not None:

                        os.close(fd)

                raise child_exception





        def _handle_exitstatus(self, sts):

            if os.WIFSIGNALED(sts):

                self.returncode = -os.WTERMSIG(sts)

            elif os.WIFEXITED(sts):

                self.returncode = os.WEXITSTATUS(sts)

            else:

                # Should never happen

                raise RuntimeError("Unknown child exit status!")





        def _internal_poll(self, _deadstate=None):

            """Check if child process has terminated.  Returns returncode

            attribute."""

            if self.returncode is None:

                try:

                    pid, sts = os.waitpid(self.pid, os.WNOHANG)

                    if pid == self.pid:

                        self._handle_exitstatus(sts)

                except os.error:

                    if _deadstate is not None:

                        self.returncode = _deadstate

            return self.returncode





        def wait(self):

            """Wait for child process to terminate.  Returns returncode

            attribute."""

            if self.returncode is None:

                pid, sts = os.waitpid(self.pid, 0)

                self._handle_exitstatus(sts)

            return self.returncode





        def _communicate(self, input):

            read_set = []

            write_set = []

            stdout = None # Return

            stderr = None # Return



            if self.stdin:

                # Flush stdio buffer.  This might block, if the user has

                # been writing to .stdin in an uncontrolled fashion.

                self.stdin.flush()

                if input:

                    write_set.append(self.stdin)

                else:

                    self.stdin.close()

            if self.stdout:

                read_set.append(self.stdout)

                stdout = []

            if self.stderr:

                read_set.append(self.stderr)

                stderr = []



            input_offset = 0

            while read_set or write_set:

                try:

                    rlist, wlist, xlist = select.select(read_set, write_set, [])

                except select.error, e:

                    if e.args[0] == errno.EINTR:

                        continue

                    raise



                if self.stdin in wlist:

                    # When select has indicated that the file is writable,

                    # we can write up to PIPE_BUF bytes without risk

                    # blocking.  POSIX defines PIPE_BUF >= 512

                    chunk = input[input_offset : input_offset + 512]

                    bytes_written = os.write(self.stdin.fileno(), chunk)

                    input_offset += bytes_written

                    if input_offset >= len(input):

                        self.stdin.close()

                        write_set.remove(self.stdin)



                if self.stdout in rlist:

                    data = os.read(self.stdout.fileno(), 1024)

                    if data == "":

                        self.stdout.close()

                        read_set.remove(self.stdout)

                    stdout.append(data)



                if self.stderr in rlist:

                    data = os.read(self.stderr.fileno(), 1024)

                    if data == "":

                        self.stderr.close()

                        read_set.remove(self.stderr)

                    stderr.append(data)



            # All data exchanged.  Translate lists into strings.

            if stdout is not None:

                stdout = ''.join(stdout)

            if stderr is not None:

                stderr = ''.join(stderr)



            # Translate newlines, if requested.  We cannot let the file

            # object do the translation: It is based on stdio, which is

            # impossible to combine with select (unless forcing no

            # buffering).

            if self.universal_newlines and hasattr(file, 'newlines'):

                if stdout:

                    stdout = self._translate_newlines(stdout)

                if stderr:

                    stderr = self._translate_newlines(stderr)



            self.wait()

            return (stdout, stderr)



        def send_signal(self, sig):

            """Send a signal to the process

            """

            os.kill(self.pid, sig)



        def terminate(self):

            """Terminate the process with SIGTERM

            """

            self.send_signal(signal.SIGTERM)



        def kill(self):

            """Kill the process with SIGKILL

            """

            self.send_signal(signal.SIGKILL)





def _demo_posix():

    #

    # Example 1: Simple redirection: Get process list

    #

    plist = Popen(["ps"], stdout=PIPE).communicate()[0]

    print "Process list:"

    print plist



    #

    # Example 2: Change uid before executing child

    #

    if os.getuid() == 0:

        p = Popen(["id"], preexec_fn=lambda: os.setuid(100))

        p.wait()



    #

    # Example 3: Connecting several subprocesses

    #

    print "Looking for 'hda'..."

    p1 = Popen(["dmesg"], stdout=PIPE)

    p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE)

    print repr(p2.communicate()[0])



    #

    # Example 4: Catch execution error

    #

    print

    print "Trying a weird file..."

    try:

        print Popen(["/this/path/does/not/exist"]).communicate()

    except OSError, e:

        if e.errno == errno.ENOENT:

            print "The file didn't exist.  I thought so..."

            print "Child traceback:"

            print e.child_traceback

        else:

            print "Error", e.errno

    else:

        print >>sys.stderr, "Gosh.  No error."





def _demo_windows():

    #

    # Example 1: Connecting several subprocesses

    #

    print "Looking for 'PROMPT' in set output..."

    p1 = Popen("set", stdout=PIPE, shell=True)

    p2 = Popen('find "PROMPT"', stdin=p1.stdout, stdout=PIPE)

    print repr(p2.communicate()[0])



    #

    # Example 2: Simple execution of program

    #

    print "Executing calc..."

    p = Popen("calc")

    p.wait()





if __name__ == "__main__":

    if mswindows:

        _demo_windows()

    else:

        _demo_posix()

