Python | Simple GUI calculator using Tkinter

Prerequisite : Tkinter Introduction, lambda function

Python offers multiple options for developing GUI (Graphical User Interface). Out of all the GUI methods, tkinter is most commonly used method. It is a standard Python interface to the Tk GUI toolkit shipped with Python. Python with tkinter outputs the fastest and easiest way to create the GUI applications. Creating a GUI using tkinter is an easy task.

To create a tkinter :



  1. Importing the module – tkinter
  2. Create the main window (container)
  3. Add any number of widgets to the main window
  4. Apply the event Trigger on the widgets.

Let’s create a GUI based simple calculator using Python Tkinter module, which can perform basic arithmatic operations addition, subtraction, multiplication and division.

Below is the implementation :

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# Python program to  create a simple GUI 
# calculator using Tkinter
  
# import everything from tkinter module
from tkinter import *
  
# globally declare the expression variable
expression = ""
  
  
# Function to update expressiom
# in the text entry box
def press(num):
    # point out the global expression variable
    global expression
  
    # concatenation of string
    expression = expression + str(num)
  
    # update the expression by using set method
    equation.set(expression)
  
  
# Function to evaluate the final expression
def equalpress():
    # Try and except statement is used
    # for handling the errors like zero
    # division error etc.
  
    # Put that code inside the try block
    # which may generate the error
    try:
  
        global expression
  
        # eval function evaluate the expression
        # and str function convert the result
        # into string
        total = str(eval(expression))
  
        equation.set(total)
  
        # initialze the expression variable
        # by empty string
        expression = ""
  
    # if error is generate then handle
    # by the except block
    except:
  
        equation.set(" error ")
        expression = ""
  
  
# Function to clear the contents
# of text entry box
def clear():
    global expression
    expression = ""
    equation.set("")
  
  
# Driver code
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("265x125")
  
    # 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)
  
    # grid method is used for placing
    # the widgets at respective positions
    # in table like structure .
    expression_field.grid(columnspan=4, ipadx=70)
  
    equation.set('enter your expression')
  
    # create a Buttons and place at a particular
    # location inside the root window .
    # when user press the button, the command or
    # function affiliated to that button is executed .
    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')
  
    # start the GUI
    gui.mainloop()

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Output :
input data     result



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