如何触发ttk.ComboboxSelected事件

Question

我只是想知道，当使用Combobox的set方法时，是否可以触发ComboboxSelected虚拟事件，就像下面代码的注释一样

import tkinter as tk
from tkinter import ttk

master = tk.Tk()

country = ttk.Combobox(master)
country['values'] = ('USA', 'Canada', 'Australia')
country.pack()

# set a default value, but it seems the value is not selected
country.set(country['values'][1])

master.mainloop()

import tkinter as tk
from tkinter import ttk

master = tk.Tk()


def select_combobox(event):

    to = int(gradations.get())
    print(to)

    for entry in entry_list[:to]:
        entry.config(state="normal")
    for entry in entry_list[to:]:
        entry.config(state="disable")


gradations = ttk.Combobox(master)
gradations['values'] = ('1', '2', '3')
gradations.bind("<<ComboboxSelected>>", select_combobox)
gradations.pack()

entry_list = []
entry1 = tk.Entry(master)
entry1.pack()
entry_list.append(entry1)
entry2 = tk.Entry(master)
entry2.pack()
entry_list.append(entry2)
entry3 = tk.Entry(master)
entry3.pack()
entry_list.append(entry3)

# gradations.set(1)

master.mainloop()