Backport patch #540583: Open MS Help Docs if available.

Tools/idle/EditorWindow.py

@@ -295,14 +295,23 @@ class EditorWindow:
     help_url = "http://www.python.org/doc/current/"
     if sys.platform[:3] == "win":
         fn = os.path.dirname(__file__)
-        fn = os.path.join(fn, os.pardir, os.pardir, "Doc", "index.html")
+        fn = os.path.join(fn, os.pardir, os.pardir, "pythlp.chm")
         fn = os.path.normpath(fn)
         if os.path.isfile(fn):
             help_url = fn
+        else:
+            fn = os.path.dirname(__file__)
+            fn = os.path.join(fn, os.pardir, os.pardir, "Doc", "index.html")
+            fn = os.path.normpath(fn)
+            if os.path.isfile(fn):
+                help_url = fn
         del fn
 
-    def python_docs(self, event=None):
-        webbrowser.open(self.help_url)
+        def python_docs(self, event=None):
+            os.startfile(self.help_url)
+    else:
+        def python_docs(self, event=None):
+            webbrowser.open(self.help_url)
 
     def select_all(self, event=None):
         self.text.tag_add("sel", "1.0", "end-1c")