Tkinter, curselection()[0], IndexError: tuple index out of range

Question

I am connecting frontend to backend of a database application using Tkinter and sqlite3.

Need help finding potential reasons that resulted in this error:

Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Users\Peng\AppData\Local\Programs\Python\Python36\lib\tkinter\__init__.py", line 1699, in __call__
    return self.func(*args)
  File "frontend.py", line 9, in get_selected_row
    index=list1.curselection()[0]
IndexError: tuple index out of range

But list1.curselection()[0] is just the id, why is it out of range?

Any help on finding where went wrong will be greatly appreciated!!!

My code:

frontend.py:

from tkinter import *
import backend
window=Tk()

list1.bind('<<ListboxSelect>>',get_selected_row)

def update_command():
    backend.update(selected_tuple[0],title_text.get()，author_text.get(),year_text.get(),isbn_text.get())

def get_selected_row(event):
    global selected_tuple
    index=list1.curselection()[0]
    selected_tuple=list1.get(index)
    e1.delete(0,END)
    e1.insert(END,selected_tuple[1])
    e2.delete(0,END)
    e2.insert(END,selected_tuple[2])
    e3.delete(0,END)
    e3.insert(END,selected_tuple[3])
    e4.delete(0,END)
    e4.insert(END,selected_tuple[4])

backend.py:

import sqlite3

def update(id,title,author,year,isbn):
    conn=sqlite3.connect("books.db")
    cur=conn.cursor()
    cur.execute("UPDATE book SET title=?,author=?,year=?,isbn=? WHERE id=?",(title,author,year,isbn,id))
    conn.commit()
    conn.close()

Answer 1

Your method is being triggered when there is nothing selected. The easiest fix is to simply check if the tuple is empty:

def get_selected_row(event):
    global selected_tuple
    index=list1.curselection()
    if index: # if the tuple is not empty
        selected_tuple=list1.get(index[0])
        e1.delete(0,END)
        e1.insert(END,selected_tuple[1])
        e2.delete(0,END)
        e2.insert(END,selected_tuple[2])
        e3.delete(0,END)
        e3.insert(END,selected_tuple[3])
        e4.delete(0,END)
        e4.insert(END,selected_tuple[4])

A more proper fix is to find out when it's being triggered like that and prevent it.

Answer 2

it happens when you click into the list1 while it is empty this is the line that triggers it

list1.bind('<<ListboxSelect>>',get_selected_row)

the solution mentioned above is suitable since you don't seem to have any other code manipulating this event however, i would word the solution a bit differently, to be consistent with your code naming conventions:

def get_selected_row(event):
    global selected_tuple
    if list1.curselection():
        index=list1.curselection()[0]
        selected_tuple=list1.get(index)
        e1.delete(0,END)
        e1.insert(END,selected_tuple[1])
        e2.delete(0,END)
        e2.insert(END,selected_tuple[2])
        e3.delete(0,END)
        e3.insert(END,selected_tuple[3])
        e4.delete(0,END)
        e4.insert(END,selected_tuple[4])