import tkinter as tk
from tkinter import ttk
from tkinter.messagebox import showinfo
from calendar import month_name

root = tk.Tk()

# config the root window
root.geometry('300x200')
root.resizable(False, False)
root.title('Combobox Widget')

# label
label = ttk.Label(text="Please select a month:")
label.pack(fill=tk.X, padx=5, pady=5)

# create a combobox
selected_month = tk.StringVar()
month_cb = ttk.Combobox(root, textvariable=selected_month)

# get first 3 letters of every month name
month_cb['values'] = [month_name[m][0:3] for m in range(1, 13)]

# prevent typing a value
month_cb['state'] = 'readonly'

# place the widget
month_cb.pack(fill=tk.X, padx=5, pady=5)


# bind the selected value changes
def month_changed(event):
    """ handle the month changed event """
    showinfo(
        title='Result',
        message=f'You selected {selected_month.get()}!'
    )

month_cb.bind('<<ComboboxSelected>>', month_changed)

root.mainloop()