self.selector = Listbox(frame)
...for item in ["lots","of","data","in","here","that","takes","up","four","lines"]:
Dots inserted to get the indenting right. Tk.END causes the interpreter to fart a syntax error and then another for every subsequent line. Every imaginable variation (with and without Tk or TK or tk, End, END, end, you get the picture) does this, or else shunts the problem into the data.
Do I have do something weird to make the snake treat the list, which makes up four lines, as a list?