"""Spawn a command with pipes to its stdin, stdout, and optionally stderr. The normal os.popen(cmd, mode) call spawns a shell command and provides afile interface to just the input or output of the process depending onwhether mode is 'r' or 'w'.  This module provides the functions popen2(cmd)and popen3(cmd) which return two or three pipes to the spawned command.""" import osimport sys __all__ = ["popen2", "popen3", "popen4"] try:    MAXFD = os.sysconf('SC_OPEN_MAX')except (AttributeError, ValueError):    MAXFD = 256 _active = [] def _cleanup():    for inst in _active[:]:        if inst.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 class Popen3:    """Class representing a child process.  Normally instances are created    by the factory functions popen2() and popen3()."""     sts = -1                    # Child not completed yet     def __init__(self, cmd, capturestderr=False, bufsize=-1):        """The parameter 'cmd' is the shell command to execute in a        sub-process.  On UNIX, 'cmd' may be a sequence, in which case arguments        will be passed directly to the program without shell intervention (as        with os.spawnv()).  If 'cmd' is a string it will be passed to the shell        (as with os.system()).   The 'capturestderr' flag, if true, specifies        that the object should capture standard error output of the child        process.  The default is false.  If the 'bufsize' parameter is        specified, it specifies the size of the I/O buffers to/from the child        process."""        _cleanup()        self.cmd = cmd        p2cread, p2cwrite = os.pipe()        c2pread, c2pwrite = os.pipe()        if capturestderr:            errout, errin = os.pipe()        self.pid = os.fork()        if self.pid == 0:            # Child            os.dup2(p2cread, 0)            os.dup2(c2pwrite, 1)            if capturestderr:                os.dup2(errin, 2)            self._run_child(cmd)        os.close(p2cread)        self.tochild = os.fdopen(p2cwrite, 'w', bufsize)        os.close(c2pwrite)        self.fromchild = os.fdopen(c2pread, 'r', bufsize)        if capturestderr:            os.close(errin)            self.childerr = os.fdopen(errout, 'r', bufsize)        else:            self.childerr = None     def __del__(self):        # In case the child hasn't been waited on, check if it's done.        self.poll(_deadstate=sys.maxint)        if self.sts < 0:            if _active is not None:                # Child is still running, keep us alive until we can wait on it.                _active.append(self)     def _run_child(self, cmd):        if isinstance(cmd, basestring):            cmd = ['/bin/sh', '-c', cmd]        for i in xrange(3, MAXFD):            try:                os.close(i)            except OSError:                pass        try:            os.execvp(cmd[0], cmd)        finally:            os._exit(1)     def poll(self, _deadstate=None):        """Return the exit status of the child process if it has finished,        or -1 if it hasn't finished yet."""        if self.sts < 0:            try:                pid, sts = os.waitpid(self.pid, os.WNOHANG)                # pid will be 0 if self.pid hasn't terminated                if pid == self.pid:                    self.sts = sts            except os.error:                if _deadstate is not None:                    self.sts = _deadstate        return self.sts     def wait(self):        """Wait for and return the exit status of the child process."""        if self.sts < 0:            pid, sts = os.waitpid(self.pid, 0)            # This used to be a test, but it is believed to be            # always true, so I changed it to an assertion - mvl            assert pid == self.pid            self.sts = sts        return self.sts  class Popen4(Popen3):    childerr = None     def __init__(self, cmd, bufsize=-1):        _cleanup()        self.cmd = cmd        p2cread, p2cwrite = os.pipe()        c2pread, c2pwrite = os.pipe()        self.pid = os.fork()        if self.pid == 0:            # Child            os.dup2(p2cread, 0)            os.dup2(c2pwrite, 1)            os.dup2(c2pwrite, 2)            self._run_child(cmd)        os.close(p2cread)        self.tochild = os.fdopen(p2cwrite, 'w', bufsize)        os.close(c2pwrite)        self.fromchild = os.fdopen(c2pread, 'r', bufsize)  if sys.platform[:3] == "win" or sys.platform == "os2emx":    # Some things don't make sense on non-Unix platforms.    del Popen3, Popen4     def popen2(cmd, bufsize=-1, mode='t'):        """Execute the shell command 'cmd' in a sub-process. On UNIX, 'cmd' may        be a sequence, in which case arguments will be passed directly to the        program without shell intervention (as with os.spawnv()). If 'cmd' is a        string it will be passed to the shell (as with os.system()). If        'bufsize' is specified, it sets the buffer size for the I/O pipes. The        file objects (child_stdout, child_stdin) are returned."""        w, r = os.popen2(cmd, mode, bufsize)        return r, w     def popen3(cmd, bufsize=-1, mode='t'):        """Execute the shell command 'cmd' in a sub-process. On UNIX, 'cmd' may        be a sequence, in which case arguments will be passed directly to the        program without shell intervention (as with os.spawnv()). If 'cmd' is a        string it will be passed to the shell (as with os.system()). If        'bufsize' is specified, it sets the buffer size for the I/O pipes. The        file objects (child_stdout, child_stdin, child_stderr) are returned."""        w, r, e = os.popen3(cmd, mode, bufsize)        return r, w, e     def popen4(cmd, bufsize=-1, mode='t'):        """Execute the shell command 'cmd' in a sub-process. On UNIX, 'cmd' may        be a sequence, in which case arguments will be passed directly to the        program without shell intervention (as with os.spawnv()). If 'cmd' is a        string it will be passed to the shell (as with os.system()). If        'bufsize' is specified, it sets the buffer size for the I/O pipes. The        file objects (child_stdout_stderr, child_stdin) are returned."""        w, r = os.popen4(cmd, mode, bufsize)        return r, welse:    def popen2(cmd, bufsize=-1, mode='t'):        """Execute the shell command 'cmd' in a sub-process. On UNIX, 'cmd' may        be a sequence, in which case arguments will be passed directly to the        program without shell intervention (as with os.spawnv()). If 'cmd' is a        string it will be passed to the shell (as with os.system()). If        'bufsize' is specified, it sets the buffer size for the I/O pipes. The        file objects (child_stdout, child_stdin) are returned."""        inst = Popen3(cmd, False, bufsize)        return inst.fromchild, inst.tochild     def popen3(cmd, bufsize=-1, mode='t'):        """Execute the shell command 'cmd' in a sub-process. On UNIX, 'cmd' may        be a sequence, in which case arguments will be passed directly to the        program without shell intervention (as with os.spawnv()). If 'cmd' is a        string it will be passed to the shell (as with os.system()). If        'bufsize' is specified, it sets the buffer size for the I/O pipes. The        file objects (child_stdout, child_stdin, child_stderr) are returned."""        inst = Popen3(cmd, True, bufsize)        return inst.fromchild, inst.tochild, inst.childerr     def popen4(cmd, bufsize=-1, mode='t'):        """Execute the shell command 'cmd' in a sub-process. On UNIX, 'cmd' may        be a sequence, in which case arguments will be passed directly to the        program without shell intervention (as with os.spawnv()). If 'cmd' is a        string it will be passed to the shell (as with os.system()). If        'bufsize' is specified, it sets the buffer size for the I/O pipes. The        file objects (child_stdout_stderr, child_stdin) are returned."""        inst = Popen4(cmd, bufsize)        return inst.fromchild, inst.tochild     __all__.extend(["Popen3", "Popen4"]) def _test():    # When the test runs, there shouldn't be any open pipes    _cleanup()    assert not _active, "Active pipes when test starts " + repr([c.cmd for c in _active])    cmd  = "cat"    teststr = "ab cd\n"    if os.name == "nt":        cmd = "more"    # "more" doesn't act the same way across Windows flavors,    # sometimes adding an extra newline at the start or the    # end.  So we strip whitespace off both ends for comparison.    expected = teststr.strip()    print "testing popen2..."    r, w = popen2(cmd)    w.write(teststr)    w.close()    got = r.read()    if got.strip() != expected:        raise ValueError("wrote %r read %r" % (teststr, got))    print "testing popen3..."    try:        r, w, e = popen3([cmd])    except:        r, w, e = popen3(cmd)    w.write(teststr)    w.close()    got = r.read()    if got.strip() != expected:        raise ValueError("wrote %r read %r" % (teststr, got))    got = e.read()    if got:        raise ValueError("unexpected %r on stderr" % (got,))    for inst in _active[:]:        inst.wait()    _cleanup()    if _active:        raise ValueError("_active not empty")    print "All OK" if __name__ == '__main__':    _test()