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  • Creating a backspace button on my calculator python tkinter GUI

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    Hello, i'm very new to python and  i would like to fix the "C" button so that it clears the last number on the display. For example 321 would become 32, i have tried a lot of things but i can't seem to get it to work, i would be very grateful if someone could get it working, thank you. Here is the code:

     

     

     

     

     

    from tkinter import *


    class Calc():
        def __init__(self):
            self.total = 0
            self.current = ""
            self.new_num = True
            self.op_pending = False
            self.op = ""
            self.eq = False


        def num_press(self, num):
            self.eq = False
            temp = text_box.get()
            temp2 = str(num)      
            if self.new_num:
                self.current = temp2
                self.new_num = False
            else:
                if temp2 == '.':
                    if temp2 in temp:
                        return
                self.current = temp + temp2
            self.display(self.current)

        def calc_total(self):
            self.eq = True
            self.current = float(self.current)
            if self.op_pending == True:
                self.do_sum()
            else:
                self.total = float(text_box.get())

        def display(self, value):
            text_box.delete(0, END)
            text_box.insert(0, value)

        def do_sum(self):
            if self.op == "add":
                self.total += self.current
            if self.op == "minus":
                self.total -= self.current
            if self.op == "times":
                self.total *= self.current
            if self.op == "divide":
                self.total /= self.current
            self.new_num = True
            self.op_pending = False
            self.display(self.total)

        def operation(self, op): 
            self.current = float(self.current)
            if self.op_pending:
                self.do_sum()
            elif not self.eq:
                self.total = self.current
            self.new_num = True
            self.op_pending = True
            self.op = op
            self.eq = False

        def cancel(self):
            self.eq = False
            self.current = "0"
            self.display(0)
            self.new_num = True

        def all_cancel(self):
            self.cancel()
            self.total = 0

        def sign(self):
            self.eq = False
            self.current = -(float(text_box.get()))
            self.display(self.current)

    sum1 = Calc()
    root = Tk()
    calc = Frame(root)
    calc.grid()

    root.title("Calculator")
    text_box = Entry(calc, justify=RIGHT)
    text_box.grid(row = 0, column = 0, columnspan = 3, pady = 5)
    text_box.insert(0, "0")

    numbers = "789456123"
    i = 0
    bttn = []
    for j in range(1,4):
        for k in range(3):
            bttn.append(Button(calc, text = numbers[i]))
            bttn[i].grid(row = j, column = k, pady = 5)
            bttn[i]["command"] = lambda x = numbers[i]: sum1.num_press(x)
            i += 1

    bttn_0 = Button(calc, text = "0")
    bttn_0["command"] = lambda: sum1.num_press(0)
    bttn_0.grid(row = 4, column = 1, pady = 5)

    bttn_div = Button(calc, text = chr(247))
    bttn_div["command"] = lambda: sum1.operation("divide")
    bttn_div.grid(row = 1, column = 3, pady = 5)

    bttn_mult = Button(calc, text = "x")
    bttn_mult["command"] = lambda: sum1.operation("times")
    bttn_mult.grid(row = 2, column = 3, pady = 5)

    minus = Button(calc, text = "-")
    minus["command"] = lambda: sum1.operation("minus")
    minus.grid(row = 3, column = 3, pady = 5)

    point = Button(calc, text = ".")
    point["command"] = lambda: sum1.num_press(".")
    point.grid(row = 4, column = 0, pady = 5)

    add = Button(calc, text = "+")
    add["command"] = lambda: sum1.operation("add")
    add.grid(row = 4, column = 3, pady = 5)

    neg= Button(calc, text = "+/-")
    neg["command"] = sum1.sign
    neg.grid(row = 5, column = 0, pady = 5)

    clear = Button(calc, text = "C")
    clear["command"] = sum1.cancel
    clear.grid(row = 5, column = 1, pady = 5)

    all_clear = Button(calc, text = "AC")
    all_clear["command"] = sum1.all_cancel
    all_clear.grid(row = 5, column = 2, pady = 5)

    equals = Button(calc, text = "=")
    equals["command"] = sum1.calc_total
    equals.grid(row = 5, column = 3, pady = 5)

    root.mainloop()
     

     

 1 Answer(s)

  • Hi friend,
    If you want to clears the last number on the display then you have to backspace then you must need remove last character in the array and function look like this (shown in below)

    def backspace_b(self):
      self.current = self.current[0:len(self.current) -1]
    
    def backspace_b(self):
          self.current = self.current[:-1]
    

    Note- When you are creating a GUI application using Tkinter ,then you have to follow below step-
    1- Import the Tkinter module.

    2- Create the GUI application main window.

    3- Add one or more of the above-mentioned widgets to the GUI application.

    4- Enter the main event loop to take action against each event triggered by the user.

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