Rip out all the u"..." literals and calls to unicode().
diff --git a/Lib/idlelib/EditorWindow.py b/Lib/idlelib/EditorWindow.py
index 7cd6c1f..7e75a6c 100644
--- a/Lib/idlelib/EditorWindow.py
+++ b/Lib/idlelib/EditorWindow.py
@@ -276,7 +276,7 @@
 
     def _filename_to_unicode(self, filename):
         """convert filename to unicode in order to display it in Tk"""
-        if isinstance(filename, unicode) or not filename:
+        if isinstance(filename, str) or not filename:
             return filename
         else:
             try: