(_spawn): New helper function, extracted from Spawn.__init__. New

	argument: use_stderr_pipe.
(Spawn.__init__): New optional argument: use_stderr_pipe.  Set the
	stderr attribute to an Expectable object that represents the
	stderr output from the subprocess it it is true.  Get rid of
	the __pty attribute, and renamed __child to __child_pid.
(Spawn.send): Use self.fileno() instead of self.__pty.
(Spawn.close): Ditto.  Close the stderr pipe if present.
(spawn2): New function.  A possibly easier API if you want to
	have the stderr output in a separate Expectable.

pcl_expect/spawn.py

@@ -7,7 +7,8 @@ import pcl_expect
 __all__ = [
     "inherit_stty",
     "stty_init",
-    "spawn",
+    "Spawn",
+    "spawn2",
     ]
 
 # When a new pty is created by spawn(), the terminal settings will be
@@ -22,8 +23,7 @@ def set_cloexec_flag(fd):
     old = fcntl.fcntl(fd, fcntl.F_GETFD)
     fcntl.fcntl(fd, fcntl.F_SETFD, old | fcntl.FD_CLOEXEC)
 
-class Spawn(pcl_expect.Expectable):
-    def __init__(self, cmd):
+def _spawn(cmd, use_stderr_pipe):
     if inherit_stty:
         f = os.popen("stty -g")
         settings = f.read()
@@ -32,37 +32,62 @@ class Spawn(pcl_expect.Expectable):
     if isinstance(cmd, basestring):
         cmd = cmd.split(" ")
     (r, w) = os.pipe()
+    if use_stderr_pipe:
+        (stderr_r, stderr_w) = os.pipe()
+    else:
+        stderr_r = None
     set_cloexec_flag(w)
-        self.__child, self.__pty = pty.fork()
-        if self.__child == 0:
+    pid, fd = pty.fork()
+    if pid == 0:
         try:
             os.close(r)
             if inherit_stty:
                 os.system("stty %s" % settings)
             if stty_init is not None:
                 os.system("stty %s" % stty_init)
+            if use_stderr_pipe:
+                os.close(stderr_r)
+                os.dup2(stderr_w, 2)
+                os.close(stderr_w)
             try:
                 os.execvp(cmd[0], cmd)
             except OSError:
+                # FIXME: transfer failure reason.
                 os.write(w, "exec failed\n")
         finally:
             os._exit(1)
-        else:
+
+    # In parent.
     os.close(w)
+    if use_stderr_pipe:
+        os.close(stderr_w)
     res = os.read(r, 100)
     os.close(r)
     if res != "":
-                os.close(self.__pty)
-                os.waitpid(self.__child, 0)
+        os.close(fd)
+        os.waitpid(pid, 0)
         raise OSError("exec failed")
-            pcl_expect.Expectable.__init__(self, self.__pty)
+    return pid, fd, stderr_r
+
+class Spawn(pcl_expect.Expectable):
+    def __init__(self, cmd, use_stderr_pipe = False):
+        self.__child_pid, fd, stderr = _spawn(cmd, use_stderr_pipe)
+        pcl_expect.Expectable.__init__(self, fd)
+        if use_stderr_pipe:
+            self.stderr = pcl_expect.Expectable(stderr)
 
     def send(self, s):
         pcl_expect.debug("sending \"%s\" to fd %d" % (s, self.fileno()))
-        os.write(self.__pty, s)
+        os.write(self.fileno(), s)
 
     def close(self):
+        os.close(self.fileno())
         pcl_expect.Expectable.close(self)
-        os.close(self.__pty)
-        return os.waitpid(self.__child, 0)
+        if hasattr(self, "stderr"):
+            os.close(self.stderr.fileno())
+            self.stderr.close()
+        return os.waitpid(self.__child_pid, 0)
 
+def spawn2(cmd):
+    proc = Spawn(cmd, True)
+    return proc, proc.stderr