diff -r 73de0794ae71 Lib/subprocess.py
--- a/Lib/subprocess.py	Mon Jun 10 23:01:20 2013 -0500
+++ b/Lib/subprocess.py	Tue Jun 11 02:00:24 2013 -0700
@@ -1243,7 +1243,7 @@
 
                             # Close pipe fds.  Make sure we don't close the
                             # same fd more than once, or standard fds.
-                            closed = { None }
+                            closed = set([None])
                             for fd in [p2cread, c2pwrite, errwrite]:
                                 if fd not in closed and fd > 2:
                                     os.close(fd)