set ttk combobox to readonly

#A Combobox is a tkinter.ttk widget equivalent to OptionMenu of tkinter but better than it. But there is a text entry in it so here is the code to disable it :
from tkinter import *
from tkinter.ttk import *
#NOTE : It is necessary to write from tkinter import * and then in next line from tkinter.ttk import * to get both tkinter and tkinter.ttk widgets.

Here is what the above code is Doing:
1. We are creating a tkinter.ttk Combobox widget.
2. We are assigning the value of the Combobox to a StringVar variable.
3. We are packing the Combobox.
4. We are running the mainloop.