text: # 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(*args, **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"])
  
  
  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.
  
  
  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 stdin 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)
  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)
  
  
  Replacing popen2.*
  ------------------
  Note: If the cmd argument to popen2 functions is a string, the command
  is executed through /bin/sh.  If it is a list, the command is directly
  executed.
  
  (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)
  
  
  (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 popen3.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
  
  if mswindows:
      import threading
      import msvcrt
      ## @@: Changed in Paste
      ## Since this module is only used on pre-python-2.4 systems, they probably
      ## don't have _subprocess installed, but hopefully have the win32 stuff
      ## installed.
      if 1: # <-- 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 win32event import WaitForSingleObject, INFINITE, WAIT_OBJECT_0
      else:
          from _subprocess import *
          class STARTUPINFO:
              dwFlags = 0
              hStdInput = None
              hStdOutput = None
              hStdError = None
          class pywintypes:
              error = IOError
  else:
      import select
      import errno
      import fcntl
      import pickle
  
  __all__ = ["Popen", "PIPE", "STDOUT", "call"]
  
  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[:]:
          inst.poll()
  
  PIPE = -1
  STDOUT = -2
  
  
  def call(*args, **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(*args, **kwargs).wait()
  
  
  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
         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)
          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 backspaces.
                  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 backspaces, 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()
  
          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:
                  raise ValueError("close_fds is not supported on Windows "
                                   "platforms")
          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 p2cwrite:
              self.stdin = os.fdopen(p2cwrite, 'wb', bufsize)
          if c2pread:
              if universal_newlines:
                  self.stdout = os.fdopen(c2pread, 'rU', bufsize)
              else:
                  self.stdout = os.fdopen(c2pread, 'rb', bufsize)
          if errread:
              if universal_newlines:
                  self.stderr = os.fdopen(errread, 'rU', bufsize)
              else:
                  self.stderr = os.fdopen(errread, 'rb', bufsize)
  
          _active.append(self)
  
  
      def _translate_newlines(self, data):
          data = data.replace("\r\n", "\n")
          data = data.replace("\r", "\n")
          return data
  
  
      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 == None and stdout == None and stderr == None:
                  return (None, None, None, None, None, None)
  
              p2cread, p2cwrite = None, None
              c2pread, c2pwrite = None, None
              errread, errwrite = None, None
  
              if stdin == None:
                  p2cread = GetStdHandle(STD_INPUT_HANDLE)
              elif stdin == PIPE:
                  p2cread, p2cwrite = CreatePipe(None, 0)
                  # Detach and turn into fd
                  p2cwrite = p2cwrite.Detach()
                  p2cwrite = msvcrt.open_osfhandle(p2cwrite, 0)
              elif type(stdin) == types.IntType:
                  p2cread = msvcrt.get_osfhandle(stdin)
              else:
                  # Assuming file-like object
                  p2cread = msvcrt.get_osfhandle(stdin.fileno())
              p2cread = self._make_inheritable(p2cread)
  
              if stdout == None:
                  c2pwrite = GetStdHandle(STD_OUTPUT_HANDLE)
              elif stdout == PIPE:
                  c2pread, c2pwrite = CreatePipe(None, 0)
                  # Detach and turn into fd
                  c2pread = c2pread.Detach()
                  c2pread = msvcrt.open_osfhandle(c2pread, 0)
              elif type(stdout) == types.IntType:
                  c2pwrite = msvcrt.get_osfhandle(stdout)
              else:
                  # Assuming file-like object
                  c2pwrite = msvcrt.get_osfhandle(stdout.fileno())
              c2pwrite = self._make_inheritable(c2pwrite)
  
              if stderr == None:
                  errwrite = GetStdHandle(STD_ERROR_HANDLE)
              elif stderr == PIPE:
                  errread, errwrite = CreatePipe(None, 0)
                  # Detach and turn into fd
                  errread = errread.Detach()
                  errread = msvcrt.open_osfhandle(errread, 0)
              elif stderr == STDOUT:
                  errwrite = c2pwrite
              elif type(stderr) == types.IntType:
                  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
              default_startupinfo = STARTUPINFO()
              if startupinfo == None:
                  startupinfo = default_startupinfo
              if not None in (p2cread, c2pwrite, errwrite):
                  startupinfo.dwFlags |= STARTF_USESTDHANDLES
                  startupinfo.hStdInput = p2cread
                  startupinfo.hStdOutput = c2pwrite
                  startupinfo.hStdError = errwrite
  
              if shell:
                  default_startupinfo.dwFlags |= STARTF_USESHOWWINDOW
                  default_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,
                                           # must inherit handles to pass std
                                           # handles
                                           1,
                                           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._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 != None:
                  p2cread.Close()
              if c2pwrite != None:
                  c2pwrite.Close()
              if errwrite != None:
                  errwrite.Close()
  
  
          def poll(self):
              """Check if child process has terminated.  Returns returncode
              attribute."""
              if self.returncode == None:
                  if WaitForSingleObject(self._handle, 0) == WAIT_OBJECT_0:
                      self.returncode = GetExitCodeProcess(self._handle)
                      _active.remove(self)
              return self.returncode
  
  
          def wait(self):
              """Wait for child process to terminate.  Returns returncode
              attribute."""
              if self.returncode == None:
                  obj = WaitForSingleObject(self._handle, INFINITE)
                  self.returncode = GetExitCodeProcess(self._handle)
                  _active.remove(self)
              return self.returncode
  
  
          def _readerthread(self, fh, buffer):
              buffer.append(fh.read())
  
  
          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)."""
              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 != 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 != None:
                  stdout = stdout[0]
              if stderr != 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(open, 'newlines'):
                  if stdout:
                      stdout = self._translate_newlines(stdout)
                  if stderr:
                      stderr = self._translate_newlines(stderr)
  
              self.wait()
              return (stdout, stderr)
  
      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 == None:
                  pass
              elif stdin == PIPE:
                  p2cread, p2cwrite = os.pipe()
              elif type(stdin) == types.IntType:
                  p2cread = stdin
              else:
                  # Assuming file-like object
                  p2cread = stdin.fileno()
  
              if stdout == None:
                  pass
              elif stdout == PIPE:
                  c2pread, c2pwrite = os.pipe()
              elif type(stdout) == types.IntType:
                  c2pwrite = stdout
              else:
                  # Assuming file-like object
                  c2pwrite = stdout.fileno()
  
              if stderr == None:
                  pass
              elif stderr == PIPE:
                  errread, errwrite = os.pipe()
              elif stderr == STDOUT:
                  errwrite = c2pwrite
              elif type(stderr) == types.IntType:
                  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):
              for i in range(3, MAXFD):
                  if i == but:
                      continue
                  try:
                      os.close(i)
                  except:
                      pass
  
  
          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]
  
              if shell:
                  args = ["/bin/sh", "-c"] + args
  
              if executable == 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()
              self._set_cloexec_flag(errpipe_write)
  
              self.pid = os.fork()
              if self.pid == 0:
                  # Child
                  try:
                      # Close parent's pipe ends
                      if p2cwrite:
                          os.close(p2cwrite)
                      if c2pread:
                          os.close(c2pread)
                      if errread:
                          os.close(errread)
                      os.close(errpipe_read)
  
                      # Dup fds for child
                      if p2cread:
                          os.dup2(p2cread, 0)
                      if c2pwrite:
                          os.dup2(c2pwrite, 1)
                      if errwrite:
                          os.dup2(errwrite, 2)
  
                      # Close pipe fds.  Make sure we doesn't close the same
                      # fd more than once.
                      if p2cread:
                          os.close(p2cread)
                      if c2pwrite and c2pwrite not in (p2cread,):
                          os.close(c2pwrite)
                      if errwrite and errwrite not in (p2cread, c2pwrite):
                          os.close(errwrite)
  
                      # Close all other fds, if asked for
                      if close_fds:
                          self._close_fds(but=errpipe_write)
  
                      if cwd != None:
                          os.chdir(cwd)
  
                      if preexec_fn:
                          apply(preexec_fn)
  
                      if env == 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
              os.close(errpipe_write)
              if p2cread and p2cwrite:
                  os.close(p2cread)
              if c2pwrite and c2pread:
                  os.close(c2pwrite)
              if errwrite and errread:
                  os.close(errwrite)
  
              # Wait for exec to fail or succeed; possibly raising exception
              data = os.read(errpipe_read, 1048576) # Exceptions limited to 1 MB
              os.close(errpipe_read)
              if data != "":
                  os.waitpid(self.pid, 0)
                  child_exception = pickle.loads(data)
                  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!")
  
              _active.remove(self)
  
  
          def poll(self):
              """Check if child process has terminated.  Returns returncode
              attribute."""
              if self.returncode == None:
                  try:
                      pid, sts = os.waitpid(self.pid, os.WNOHANG)
                      if pid == self.pid:
                          self._handle_exitstatus(sts)
                  except os.error:
                      pass
              return self.returncode
  
  
          def wait(self):
              """Wait for child process to terminate.  Returns returncode
              attribute."""
              if self.returncode == None:
                  pid, sts = os.waitpid(self.pid, 0)
                  self._handle_exitstatus(sts)
              return self.returncode
  
  
          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)."""
              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 = []
  
              while read_set or write_set:
                  rlist, wlist, xlist = select.select(read_set, write_set, [])
  
                  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
                      bytes_written = os.write(self.stdin.fileno(), input[:512])
                      input = input[bytes_written:]
                      if not 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 != None:
                  stdout = ''.join(stdout)
              if stderr != 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(open, 'newlines'):
                  if stdout:
                      stdout = self._translate_newlines(stdout)
                  if stderr:
                      stderr = self._translate_newlines(stderr)
  
              self.wait()
              return (stdout, stderr)
  
  
  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()
  