Document os.device_encoding.
diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index 4dbeac3..2a8325a 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -401,6 +401,12 @@
:func:`fdopen`, use its :meth:`close` method.
+.. function:: device_encoding(fd)
+
+ Return a string describing the encoding of the device associated with *fd*
+ if it is connected to a terminal; else return :const:`None`.
+
+
.. function:: dup(fd)
Return a duplicate of file descriptor *fd*. Availability: Macintosh, Unix,