Adding a CLEAR ENTRY button in TKINTER CALCULATOR

Question

I am writing a calculator, in Tkinter (Python). I want to add a CLEAR ENTRY button, that clears the 'entry' user gives. Don't get confused with the CLEAR ALL button.

Example: User enters:- 35+87=62 and presses the CE button, so he should be displayed:- 35+87 and if he presses it again, he should get 35 and so on till 0.

I have tried a lot, in the end, I came to you. Here is the basic code, (It does not have any CE button made, you can add one). You can use regex.

from tkinter import *
expression = "" 
def press(num): 
    global expression 
    expression = expression + str(num) 
    equation.set(expression) 
  
  

def equalpress(): 
    try: 
        global expression 
        total = str(eval(expression)) 
        equation.set(total) 
        expression = "" 
    except: 
        equation.set(" error ") 
        expression = "" 
def clear(): 
    global expression 
    expression = "" 
    equation.set("") 
  

if __name__ == "__main__": 
    # create a GUI window 
    gui = Tk() 
  
    # set the background colour of GUI window 
    gui.configure(background="light green") 
  
    # set the title of GUI window 
    gui.title("Simple Calculator") 
  
    # set the configuration of GUI window 
    gui.geometry("270x150") 
  
    # StringVar() is the variable class 
    # we create an instance of this class 
    equation = StringVar() 
  
    # create the text entry box for 
    # showing the expression . 
    expression_field = Entry(gui, textvariable=equation) 
  
    expression_field.grid(columnspan=4, ipadx=70) 
  
    equation.set('enter your expression') 
  
    button1 = Button(gui, text=' 1 ', fg='black', bg='red', 
                     command=lambda: press(1), height=1, width=7) 
    button1.grid(row=2, column=0) 
  
    button2 = Button(gui, text=' 2 ', fg='black', bg='red', 
                     command=lambda: press(2), height=1, width=7) 
    button2.grid(row=2, column=1) 
  
    button3 = Button(gui, text=' 3 ', fg='black', bg='red', 
                     command=lambda: press(3), height=1, width=7) 
    button3.grid(row=2, column=2) 
  
    button4 = Button(gui, text=' 4 ', fg='black', bg='red', 
                     command=lambda: press(4), height=1, width=7) 
    button4.grid(row=3, column=0) 
  
    button5 = Button(gui, text=' 5 ', fg='black', bg='red', 
                     command=lambda: press(5), height=1, width=7) 
    button5.grid(row=3, column=1) 
  
    button6 = Button(gui, text=' 6 ', fg='black', bg='red', 
                     command=lambda: press(6), height=1, width=7) 
    button6.grid(row=3, column=2) 
  
    button7 = Button(gui, text=' 7 ', fg='black', bg='red', 
                     command=lambda: press(7), height=1, width=7) 
    button7.grid(row=4, column=0) 
  
    button8 = Button(gui, text=' 8 ', fg='black', bg='red', 
                     command=lambda: press(8), height=1, width=7) 
    button8.grid(row=4, column=1) 
  
    button9 = Button(gui, text=' 9 ', fg='black', bg='red', 
                     command=lambda: press(9), height=1, width=7) 
    button9.grid(row=4, column=2) 
  
    button0 = Button(gui, text=' 0 ', fg='black', bg='red', 
                     command=lambda: press(0), height=1, width=7) 
    button0.grid(row=5, column=0) 
  
    plus = Button(gui, text=' + ', fg='black', bg='red', 
                  command=lambda: press("+"), height=1, width=7) 
    plus.grid(row=2, column=3) 
  
    minus = Button(gui, text=' - ', fg='black', bg='red', 
                   command=lambda: press("-"), height=1, width=7) 
    minus.grid(row=3, column=3) 
  
    multiply = Button(gui, text=' * ', fg='black', bg='red', 
                      command=lambda: press("*"), height=1, width=7) 
    multiply.grid(row=4, column=3) 
  
    divide = Button(gui, text=' / ', fg='black', bg='red', 
                    command=lambda: press("/"), height=1, width=7) 
    divide.grid(row=5, column=3) 
  
    equal = Button(gui, text=' = ', fg='black', bg='red', 
                   command=equalpress, height=1, width=7) 
    equal.grid(row=5, column=2) 
  
    clear = Button(gui, text='Clear', fg='black', bg='red', 
                   command=clear, height=1, width=7) 
    clear.grid(row=5, column='1') 
  
    Decimal= Button(gui, text='.', fg='black', bg='red', 
                    command=lambda: press('.'), height=1, width=7) 
    Decimal.grid(row=6, column=0) 
    gui.mainloop() 

Answer 1

In the equation field, only numbers, operators and the decimal point are allowed. To clear the latest entry, search from the end of the equation for the first operator (+ - * /) then truncate the string.

Use this function for the ClearEntry button:

def clearentry(): 
    global expression 
    for i,c in enumerate(expression[::-1]): # reverse string
       if c in ['+','-','/','*']:  # find first operator 
           expression = expression[:-i-1]  # truncate string
           break
    else:
      expression = "" # no operator found
    equation.set(expression)