Use the with statement to open a file.

IPython/core/magics/code.py

@@ -402,9 +402,8 b' class CodeMagics(Magics):'
         self.shell.hooks.editor(filename)
 
         # and make a new macro object, to replace the old one
-        mfile = open(filename)
-        mvalue = mfile.read()
-        mfile.close()
+        with open(filename) as mfile:
+            mvalue = mfile.read()
         self.shell.user_ns[mname] = Macro(mvalue)
 
     @skip_doctest