Python | Simple calculator using Tkinter

Last Updated : 15 Jul, 2021

Prerequisite : Tkinter Introduction
Python offers multiple options for developing GUI (Graphical User Interface). Out of all the GUI methods, tkinter is the 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.
Let's see how to create a basic calculator using Tkinter.

Basic steps:

First we create an object named root out of tk.
We create an object of the calc and pass root as master to the init method.
Mainloop starts an event loop, which is basically an infinite loop waiting for events and respond accordingly. The mainloop can be terminated by closing the window or using close method.

Below is the implementation:

Python3

# importing Tkinter and math
from tkinter import *
import math

# calc class
class calc:

    def getandreplace(self):

        """replace x with * and ÷ with /"""
        self.expression = self.e.get()
        self.newtext=self.expression.replace('/','/')
        self.newtext=self.newtext.replace('x','*')


    def equals(self):
        """when the equal button is pressed"""
        self.getandreplace()
        try:
            # evaluate the expression using the eval function
            self.value= eval(self.newtext) 
        except SyntaxError or NameError:
            self.e.delete(0,END)
            self.e.insert(0,'Invalid Input!')
        else:
            self.e.delete(0,END)
            self.e.insert(0,self.value)

    def squareroot(self):
        """squareroot method"""
        self.getandreplace()
        try:
            # evaluate the expression using the eval function
            self.value= eval(self.newtext) 
        except SyntaxError or NameError:
            self.e.delete(0,END)
            self.e.insert(0,'Invalid Input!')
        else:
            self.sqrtval=math.sqrt(self.value)
            self.e.delete(0,END)
            self.e.insert(0,self.sqrtval)

    def square(self):
        """square method"""
        self.getandreplace()
        try:
            #evaluate the expression using the eval function
            self.value= eval(self.newtext) 
        except SyntaxError or NameError:
            self.e.delete(0,END)
            self.e.insert(0,'Invalid Input!')
        else:
            self.sqval=math.pow(self.value,2)
            self.e.delete(0,END)
            self.e.insert(0,self.sqval)

    def clearall(self):
            """when clear button is pressed,clears the text input area"""
            self.e.delete(0,END)

    def clear1(self):
            self.txt=self.e.get()[:-1]
            self.e.delete(0,END)
            self.e.insert(0,self.txt)

    def action(self,argi):
            """pressed button's value is inserted into the end of the text area"""
            self.e.insert(END,argi)

    def __init__(self,master):
            """Constructor method"""
            master.title('Calculator')
            master.geometry()
            self.e = Entry(master)
            self.e.grid(row=0,column=0,columnspan=6,pady=3)
            self.e.focus_set() #Sets focus on the input text area

            # Generating Buttons
            Button(master,text="=",width=11,height=3,fg="blue",
                   bg="orange",command=lambda:self.equals()).grid(
                                     row=4, column=4,columnspan=2)

            Button(master,text='AC',width=5,height=3,
                          fg="red", bg="light green",
             command=lambda:self.clearall()).grid(row=1, column=4)

            Button(master,text='C',width=5,height=3,
                   fg="red",bg="light green",
                   command=lambda:self.clear1()).grid(row=1, column=5)

            Button(master,text="+",width=5,height=3,
                   fg="blue",bg="orange",
                   command=lambda:self.action('+')).grid(row=4, column=3)

            Button(master,text="x",width=5,height=3,
                    fg="blue",bg="orange",
                    command=lambda:self.action('x')).grid(row=2, column=3)

            Button(master,text="-",width=5,height=3,
                    fg="red",bg="light green",
                    command=lambda:self.action('-')).grid(row=3, column=3)

            Button(master,text="÷",width=5,height=3,
                   fg="blue",bg="orange",
                   command=lambda:self.action('/')).grid(row=1, column=3)

            Button(master,text="%",width=5,height=3,
                   fg="red",bg="light green",
                   command=lambda:self.action('%')).grid(row=4, column=2)

            Button(master,text="7",width=5,height=3,
                   fg="blue",bg="orange",
                   command=lambda:self.action('7')).grid(row=1, column=0)

            Button(master,text="8",width=5,height=3,
                   fg="red",bg="light green",
                   command=lambda:self.action(8)).grid(row=1, column=1)

            Button(master,text="9",width=5,height=3,
                   fg="blue",bg="orange",
                   command=lambda:self.action(9)).grid(row=1, column=2)

            Button(master,text="4",width=5,height=3,
                   fg="red",bg="light green",
                   command=lambda:self.action(4)).grid(row=2, column=0)

            Button(master,text="5",width=5,height=3,
                   fg="blue",bg="orange",
                   command=lambda:self.action(5)).grid(row=2, column=1)

            Button(master,text="6",width=5,height=3,
                   fg="white",bg="blue",
                   command=lambda:self.action(6)).grid(row=2, column=2)

            Button(master,text="1",width=5,height=3,
                   fg="red",bg="light green",
                   command=lambda:self.action(1)).grid(row=3, column=0)

            Button(master,text="2",width=5,height=3,
                   fg="blue",bg="orange",
                   command=lambda:self.action(2)).grid(row=3, column=1)

            Button(master,text="3",width=5,height=3,
                   fg="white",bg="blue",
                   command=lambda:self.action(3)).grid(row=3, column=2)

            Button(master,text="0",width=5,height=3,
                   fg="white",bg="blue",
                   command=lambda:self.action(0)).grid(row=4, column=0)

            Button(master,text=".",width=5,height=3,
                   fg="red",bg="light green",
                   command=lambda:self.action('.')).grid(row=4, column=1)

            Button(master,text="(",width=5,height=3,
                   fg="white",bg="blue",
                   command=lambda:self.action('(')).grid(row=2, column=4)

            Button(master,text=")",width=5,height=3,
                   fg="blue",bg="orange",
                   command=lambda:self.action(')')).grid(row=2, column=5)

            Button(master,text="?",width=5,height=3,
                   fg="red",bg="light green",
                   command=lambda:self.squareroot()).grid(row=3, column=4)

            Button(master,text="x²",width=5,height=3,
                   fg="white",bg="blue",
                   command=lambda:self.square()).grid(row=3, column=5)

# Driver Code
root = Tk()

obj=calc(root) # object instantiated

root.mainloop()