Index: Doc/library/os.rst
===================================================================
--- Doc/library/os.rst	(revision 86560)
+++ Doc/library/os.rst	(working copy)
@@ -1792,11 +1792,13 @@
    Availability: Unix.
 
 
-.. function:: popen(...)
-   :noindex:
+.. function:: popen(command[, mode[, buffering]])
 
-   Run child processes, returning opened pipes for communications.  These functions
-   are described in section :ref:`os-newstreams`.
+   Open a pipe to or from *command*.  The return value is an open file object
+   connected to the pipe, which can be read or written depending on whether *mode*
+   is ``'r'`` (default) or ``'w'``. The *buffering* argument has the same meaning as
+   the corresponding argument to the built-in :func:`open` function. This is
+   implemented using :class:`subprocess.Popen`,
 
 
 .. function:: spawnl(mode, path, ...)