Index: Doc/library/os.rst
===================================================================
--- Doc/library/os.rst	(revision 79421)
+++ Doc/library/os.rst	(working copy)
@@ -437,7 +437,10 @@
 is slightly deceptive; on Unix platforms, sockets and pipes are also referenced
 by file descriptors.
 
+The fileno() method can be used to obtain the file descriptor associated with
+a file object when required.
 
+
 .. function:: close(fd)
 
    Close file descriptor *fd*. Availability: Unix, Windows.