Follow-up to #4488: document PIPE and STDOUT properly.

Doc/library/subprocess.rst

@@ -73,13 +73,13 @@ This module defines one class called :class:`Popen`:
    specified by the :envvar:`COMSPEC` environment variable.
 
    *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.
+   standard output and standard error file handles, respectively.  Valid values
+   are :data:`PIPE`, an existing file descriptor (a positive integer), an
+   existing file object, and ``None``.  :data:`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 :data:`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. (Unix only)
@@ -119,6 +119,20 @@ This module defines one class called :class:`Popen`:
    of the main window and priority for the new process.  (Windows only)
 
 
+.. data:: PIPE
+
+   Special value that can be used as the *stdin*, *stdout* or *stderr* argument
+   to :class:`Popen` and indicates that a pipe to the standard stream should be
+   opened.
+
+
+.. data:: STDOUT
+
+   Special value that can be used as the *stderr* argument to :class:`Popen` and
+   indicates that standard error should go into the same handle as standard
+   output.
+   
+
 Convenience Functions
 ^^^^^^^^^^^^^^^^^^^^^
 
@@ -285,20 +299,21 @@ The following attributes are also available:
 
 .. attribute:: Popen.stdin
 
-   If the *stdin* argument is ``PIPE``, this attribute is a file object that
-   provides input to the child process.  Otherwise, it is ``None``.
+   If the *stdin* argument was :data:`PIPE`, this attribute is a file object
+   that provides input to the child process.  Otherwise, it is ``None``.
 
 
 .. attribute:: Popen.stdout
 
-   If the *stdout* argument is ``PIPE``, this attribute is a file object that
-   provides output from the child process.  Otherwise, it is ``None``.
+   If the *stdout* argument was :data:`PIPE`, this attribute is a file object
+   that provides output from the child process.  Otherwise, it is ``None``.
 
 
 .. attribute:: Popen.stderr
 
-   If the *stderr* argument is ``PIPE``, this attribute is file object that
-   provides error output from the child process.  Otherwise, it is ``None``.
+   If the *stderr* argument was :data:`PIPE`, this attribute is a file object
+   that provides error output from the child process.  Otherwise, it is
+   ``None``.
 
 
 .. attribute:: Popen.pid
@@ -478,15 +493,15 @@ Replacing functions from the popen2 module
              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:
+:class:`popen2.Popen3` and :class:`popen2.Popen4` basically work as
+:class:`subprocess.Popen`, except that:
 
-* subprocess.Popen raises an exception if the execution fails
+* :class:`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.
+* ``stdin=PIPE`` and ``stdout=PIPE`` must be specified.
 
 * popen2 closes all file descriptors by default, but you have to specify
-  close_fds=True with subprocess.Popen.
+  ``close_fds=True`` with :class:`Popen`.