Index: Lib/os.py
===================================================================
--- Lib/os.py	(revision 66050)
+++ Lib/os.py	(working copy)
@@ -753,8 +753,10 @@
             _urandomfd = open("/dev/urandom", O_RDONLY)
         except (OSError, IOError):
             raise NotImplementedError("/dev/urandom (or equivalent) not found")
-        bytes = ""
-        while len(bytes) < n:
-            bytes += read(_urandomfd, n - len(bytes))
-        close(_urandomfd)
-        return bytes
+        try:
+            bs = b""
+            while n - len(bs) >= 1:
+                bs += read(_urandomfd, n - len(bs))
+        finally:
+            close(_urandomfd)
+        return bs
Index: Lib/test/test_os.py
===================================================================
--- Lib/test/test_os.py	(revision 66050)
+++ Lib/test/test_os.py	(working copy)
@@ -497,6 +497,10 @@
             self.assertEqual(len(os.urandom(10)), 10)
             self.assertEqual(len(os.urandom(100)), 100)
             self.assertEqual(len(os.urandom(1000)), 1000)
+            # see http://bugs.python.org/issue3708
+            self.assertEqual(len(os.urandom(0.9)), 0)
+            self.assertEqual(len(os.urandom(1.1)), 1)
+            self.assertEqual(len(os.urandom(2.0)), 2)
         except NotImplementedError:
             pass