tkinter_calculator.py

from tkinter import *
import ast

root = Tk()

i = 0
def get_number(num):
    global i
    display.insert(i, num)
    i+=1

def get_operation(operator):
    global i
    length = len(operator)
    display.insert(i, operator)
    i += length

def clear_all():
    display.delete(0, END)

def calculate():
    entire_string = display.get()
    try:
        node = ast.parse(entire_string, mode = "eval")
        result = eval(compile(node, '<string>', 'eval'))
        clear_all()
        display.insert(0, result)
    except Exception:
        clear_all()
        display.insert(0, "Error")

def undo():
    entire_string = display.get()
    if len(entire_string):
        new_string = entire_string[:-1]
        clear_all()
        display.insert(0,new_string)
    else:
        clear_all()
        display.insert(0,"")


display = Entry(root)
display.grid(row = 1, columnspan = 6)

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9]
counter = 0


for x in range(3):
    for y in range(3):
        button_text = numbers[counter]
        button = Button(root, text = button_text, width = 2, height = 2, command = lambda text = button_text: get_number(text))
        button.grid(row = x + 2 , column = y)
        counter += 1

button = Button(root, text = "0", width = 2, height = 2, command = lambda : get_number(0))
button.grid(row = 5, column = 1)

operations = ['+', '-', '*', '/', '*3.14', '%', '(', '**', ')', '**2']
count = 0
for x in range(4):
    for y in range(3):
        if count<len(operations):
            button = Button(root, text = operations[count], width = 2, height = 2, command = lambda operator = operations[count]: get_operation(operator))
            count +=1
            button.grid(row = x+2, column = y+3)

Button(root, text = "AC", width = 2, height = 2, command = clear_all).grid(row = 5, column = 0)
Button(root, text = "=", width = 2, height = 2, command = calculate).grid(row = 5, column = 2)
Button(root, text="<-", width=2, height=2, command=lambda: undo()).grid(row=5, column=4)


root.mainloop()