What's New in Python 3.5: document os.urandom() changes

Doc/library/os.rst

@@ -3730,3 +3730,9 @@ Miscellaneous Functions
 
    For an easy-to-use interface to the random number generator
    provided by your platform, please see :class:`random.SystemRandom`.
+
+   .. versionchanged:: 3.5
+      On Linux 3.17 and newer, the ``getrandom()`` syscall is now used
+      when available.  On OpenBSD 5.6 and newer, the C ``getentropy()``
+      function is now used. These functions avoid the usage of an internal file
+      descriptor.

Doc/whatsnew/3.5.rst

@@ -648,6 +648,11 @@ os
 * :class:`os.stat_result` now has a :attr:`~os.stat_result.st_file_attributes`
   attribute on Windows.  (Contributed by Ben Hoyt in :issue:`21719`.)
 
+* :func:`os.urandom`: On Linux 3.17 and newer, the ``getrandom()`` syscall is
+  now used when available. On OpenBSD 5.6 and newer, the C ``getentropy()``
+  function is now used. These functions avoid the usage of an internal file
+  descriptor.
+
 os.path
 -------