NameError: global name 'END' is not defined

Question

I have found this code about scrollbar is just working fine.

from tkinter import *

master = Tk()

scrollbar = Scrollbar(master)
scrollbar.pack(side=RIGHT, fill=Y)

listbox = Listbox(master, yscrollcommand=scrollbar.set)
for i in range(10000):
    listbox.insert(END, str(i))
listbox.pack(side=LEFT, fill=BOTH)

scrollbar.config(command=listbox.yview)

mainloop()

I try to use it in my code like this:

import tkinter as tk

class interface(tk.Frame):
    def __init__(self,den):
        self.tklist() 
        #in my code, tklist is not called here. I called it here to minimize the code
        #there are stuff in here also

    def tklist(self):
        scrollbar = tk.Scrollbar(den)
        self.lst1 = tk.Listbox(den, selectmode="SINGLE", width="100", yscrollcommand=scrollbar.set)
        for i in range(1000):
            self.lst1.insert(END, str(i))
        self.lst1.pack(side=LEFT, fill=BOTH)
        scrollbar.config(command=lst1.yview)

den = tk.Tk()
den.title("Search")

inter = interface(den)

den.mainloop()

But when I ran above code, I got an error on insertion line.

NameError: global name 'END' is not defined

By the way, I tried to find documentation and a link from effbot is the closest I got but still couldn't understand what is wrong.