Program 10: Create a graphical application that accepts user inputs, performs some operation on them, and then writes the output on the screen. For example, write a small calculator. Use the tkinter library

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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='blue', bg='black', 
        command=lambda: press(1), height=1, width=7) 
    button1.grid(row=2, column=0) 

    button2 = Button(gui, text=' 2 ', fg='blue', bg='black', 
        command=lambda: press(2), height=1, width=7) 
    button2.grid(row=2, column=1) 

    button3 = Button(gui, text=' 3 ', fg='blue', bg='black', 
        command=lambda: press(3), height=1, width=7) 
    button3.grid(row=2, column=2) 

    button4 = Button(gui, text=' 4 ', fg='blue', bg='black', 
        command=lambda: press(4), height=1, width=7) 
    button4.grid(row=3, column=0) 

    button5 = Button(gui, text=' 5 ', fg='blue', bg='black', 
        command=lambda: press(5), height=1, width=7) 
    button5.grid(row=3, column=1) 

    button6 = Button(gui, text=' 6 ', fg='blue', bg='black', 
        command=lambda: press(6), height=1, width=7) 
    button6.grid(row=3, column=2) 

    button7 = Button(gui, text=' 7 ', fg='blue', bg='black', 
        command=lambda: press(7), height=1, width=7) 
    button7.grid(row=4, column=0) 

    button8 = Button(gui, text=' 8 ', fg='blue', bg='black', 
        command=lambda: press(8), height=1, width=7) 
    button8.grid(row=4, column=1) 

    button9 = Button(gui, text=' 9 ', fg='blue', bg='black', 
        command=lambda: press(9), height=1, width=7) 
    button9.grid(row=4, column=2) 

    button0 = Button(gui, text=' 0 ', fg='blue', bg='black', 
        command=lambda: press(0), height=1, width=7) 
    button0.grid(row=5, column=0) 

    plus = Button(gui, text=' + ', fg='blue', bg='black', 
        command=lambda: press("+"), height=1, width=7) 
    plus.grid(row=2, column=3) 

    minus = Button(gui, text=' - ', fg='blue', bg='black', 
        command=lambda: press("-"), height=1, width=7) 
    minus.grid(row=3, column=3) 

    multiply = Button(gui, text=' * ', fg='blue', bg='black', 
        command=lambda: press("*"), height=1, width=7) 
    multiply.grid(row=4, column=3) 

    divide = Button(gui, text=' / ', fg='blue', bg='black', 
        command=lambda: press("/"), height=1, width=7) 
    divide.grid(row=5, column=3) 

    equal = Button(gui, text=' = ', fg='blue', bg='black', 
        command=equalpress, height=1, width=7) 
    equal.grid(row=5, column=2) 

    clear = Button(gui, text='Clear', fg='blue', bg='black', 
        command=clear, height=1, width=7) 
    clear.grid(row=5, column='1') 

    # start the GUI 
    gui.mainloop()