Fix for issue5194, based on a patch by Ned Deily.
diff --git a/Lib/idlelib/keybindingDialog.py b/Lib/idlelib/keybindingDialog.py
index f5d32ef..b99c5e0 100644
--- a/Lib/idlelib/keybindingDialog.py
+++ b/Lib/idlelib/keybindingDialog.py
@@ -4,6 +4,7 @@
 from tkinter import *
 import tkinter.messagebox as tkMessageBox
 import string
+from idlelib import macosxSupport
 
 class GetKeysDialog(Toplevel):
     def __init__(self,parent,title,action,currentKeySequences):
@@ -133,7 +134,7 @@
         config-keys.def must use the same ordering.
         """
         import sys
-        if sys.platform == 'darwin' and sys.argv[0].count('.app'):
+        if macosxSupport.runningAsOSXApp():
             self.modifiers = ['Shift', 'Control', 'Option', 'Command']
         else:
             self.modifiers = ['Control', 'Alt', 'Shift']