IPython/utils/io.py: Make sure `devnull` is closed at exit to avoid a `ResourceWarning` being raised by Python 3.

IPython/utils/io.py

@@ -10,6 +10,7 b' from __future__ import print_function'
 from __future__ import absolute_import
 
 
+import atexit
 import os
 import sys
 import tempfile
@@ -73,6 +74,7 b' class IOStream:'
 
 # setup stdin/stdout/stderr to sys.stdin/sys.stdout/sys.stderr
 devnull = open(os.devnull, 'w') 
+atexit.register(devnull.close)
 stdin = IOStream(sys.stdin, fallback=devnull)
 stdout = IOStream(sys.stdout, fallback=devnull)
 stderr = IOStream(sys.stderr, fallback=devnull)