NameError: name 'second_number' is not defined in tkinter

Question

I'm working on a calculator GUI. I've finished working on the GUI itself and now I'm working on making the calc perform operations. It's supposed to perform addition, subtraction, multiplication and division, and squares. But I keep getting this error which is bugging me.

Traceback (most recent call last):
File "C:\Users\Admin\Python3.9\lib\tkinter\__init__.py", line 1892, in __call__
return self.func(*args)
File "C:\Users\Admin\PycharmProjects\pythonProject\Calculator GUI v1.0.py", line 57, in 
button_equal
e.insert(0, f_num) + int(second_number)
NameError: name 'second_number' is not defined

Process finished with exit code 0

My code:

import tkinter as Tk
from tkinter import *

root_var = Tk()
root_var.title("Calculator")

e = Entry(root_var, width=25, borderwidth=5)
e.grid(row=0, column=0, columnspan=3, padx=10, pady=10)

def button_click(number=None):

#e.delete(0, END)
current = e.get()
e.delete(0, END)
e.insert(0, str(current) + str(number) )

def button_clear():
e.delete(0, END)


def button_add():
first_number = e.get()
global f_num
f_num = int(first_number)
e.delete(0, END)


def button_subtract():
second_number = e.get()
e.delete(0, END)
e.insert(0, f_num + int(second_number))


def button_multiply():
third_number = e.get()
e.delete(0, END)
e.insert(0, f_num + int(third_number))



def button_divide():
fourth_number = e.get()
e.delete(0, END)
e.insert(0, f_num + int(fourth_number))



def button_exponents():
fifth_number = e.get()
e.delete(0, END)
e.insert(0, f_num + int(fifth_number))

def button_equal():
sixth_number = e.get()
e.delete(0, END)
e.insert(0, f_num) + int(second_number)

button_1 = Button(root_var, text="1", padx=50, pady=10, command=lambda: button_click(1))
button_2 = Button(root_var, text="2", padx=50, pady=10, command=lambda: button_click(2))
button_3 = Button(root_var, text="3", padx=50, pady=10, command=lambda: button_click(3))
button_4 = Button(root_var, text="4", padx=50, pady=10, command=lambda: button_click(4))
button_5 = Button(root_var, text="5", padx=50, pady=10, command=lambda: button_click(5))
button_6 = Button(root_var, text="6", padx=50, pady=10, command=lambda: button_click(6))
button_7 = Button(root_var, text="7", padx=50, pady=10, command=lambda: button_click(7))
button_8 = Button(root_var, text="8", padx=50, pady=10, command=lambda: button_click(8))
button_9 = Button(root_var, text="9", padx=50, pady=10, command=lambda: button_click(9))
button_0 = Button(root_var, text="0", padx=50, pady=10, command=lambda: button_click(0))

button_addition = Button(root_var, text="+", padx=50, pady=10, command=button_add)
button_subtraction = Button(root_var, text="-", padx=50, pady=10, command=button_subtract)
button_multiplication = Button(root_var, text="*", padx=50, pady=10, command=button_multiply)
button_division = Button(root_var, text="/", padx=50, pady=10, command=button_divide)
button_exponents = Button(root_var, text="^", padx=50, pady=10, command=button_exponents)

button_equals = Button(root_var, text="=", padx=50, pady=10, command=button_equal)

button_clear = Button(root_var, text="C", padx=50, pady=10, command=button_clear)

button_1.grid(row=3, column=2)
button_2.grid(row=3, column=1)
button_3.grid(row=3, column=0)

button_4.grid(row=2, column=2)
button_5.grid(row=2, column=1)
button_6.grid(row=2, column=0)

button_7.grid(row=1, column=2)
button_8.grid(row=1, column=1)
button_9.grid(row=1, column=0)

button_0.grid(row=4, column=0)
button_addition.grid(row=4, column=1)
button_subtraction.grid(row=4, column=2)

button_multiplication.grid(row=5, column=0)
button_division.grid(row=5, column=1)
button_exponents.grid(row=5, column=2)

button_equals.grid(row=6, column=0)
button_clear.grid(row=6, column=1)


 root_var.mainloop()

Please help me out. Thanks!

Answer 1

You're using second_number instead of sixth_number

def button_equal():  
    sixth_number = e.get()
    e.delete(0, END)
    e.insert(0, f_num) + int(sixth_number)

EDIT: Change

e.insert(0, f_num) + int(sixth_number) 

to

e.insert(0, f_num + int(sixth_number))

The first way you're summing the return of e.insert() plus sixth_number (so, you will get a TypeError, because you're trying to sum a None and Int).

The second way you're summing f_num plus sixth_number, and then insert the result into the Entry «e».