Issue 24759: Gracefull exit Idle if ttk import fails.

Author: terryjreedy

Lib/idlelib/PyShell.py

@@ -23,6 +23,16 @@
           "Your Python may not be configured for Tk. **", file=sys.__stderr__)
     sys.exit(1)
 import tkMessageBox
+try:
+    import ttk
+except:
+    root = Tk()
+    root.withdraw()
+    tkMessageBox.showerror("Idle Cannot Start",
+            "Idle now requires the Tkinter ttk module from tcl/tk 8.5+.\n"
+            + "It found tk %s and no ttk." % TkVersion,
+            parent=root)
+    sys.exit(1)
 
 from idlelib.EditorWindow import EditorWindow, fixwordbreaks
 from idlelib.FileList import FileList