Tkinter, step 2: adapt imports.
diff --git a/Lib/tkinter/messagebox.py b/Lib/tkinter/messagebox.py
index 94ba788b..c934956 100644
--- a/Lib/tkinter/messagebox.py
+++ b/Lib/tkinter/messagebox.py
@@ -22,7 +22,7 @@
 # - type: dialog type; that is, which buttons to display (see below)
 #
 
-from tkCommonDialog import Dialog
+from tkinter.commondialog import Dialog
 
 #
 # constants