Python - Dynamic GUI Calculator using Tkinter module

Last Updated : 14 Aug, 2021

Python provides many options for developing GUI like Kivy, PyQT, WxPython, and several others. Tkinter is the one that is shipped inbuilt with python which makes it the most commonly used out of all. Tkinter is easy, fast, and powerful.

Beginners can easily learn to create a simple calculator using this article: Python | Simple GUI calculator using Tkinter

The simple calculator created by manually adding each button and creating different functions for each unique button is a tedious task. It is not the best practice. Here we will see a dynamic calculator program that can be easily scaled. Let us create a simple and easy GUI calculator that can do basic math operations like multiplication, division, square root, addition, and subtraction, even more operations can be added, and according to it changes can be made in the function.

Step-by-step Approach:

Creating the main window
Creating a container containing all keys used in the calculator (Here List)
Creating a container for all our buttons created
Creating buttons and adding them to the button container
Defining the function to be called when a button is pressed
Running the main loop

Below is the implementation of the above approach:

Python3

# Import required modules
from tkinter import *
import tkinter.font as font



# Creating the main window
root = Tk()

# Assigning it the desired geometry
root.geometry("380x400")

# Assigning the name of our window
root.title("Calculator")

# Assigning it the capability to 
# be resizable (It is default)
root.resizable(0, 0)

# Creating a StringVar to take 
# the text entered in the Entry widget
inp = StringVar()
myFont = font.Font(size=15)

# Creating an Entry widget to get the 
# mathematical expression
# And also to display the results
screen = Entry(root, text=inp, width=30, 
               justify='right', font=(10), bd=4)

# We will use a grid like structure
screen.grid(row=0, columnspan=4, padx=15,
            pady=15, ipady=5)

# Key matrix contains all the required the keys
key_matrix = [["c", u"\u221A", "/", "<-"], 
              ["7", "8", "9", "*"],
              ["4", "5", "6", "-"], 
              ["1", "2", "3", "+"],
              ["!", 0, ".", "="]]

# Creating a dictionary for the buttons
btn_dict = {}

# Variable to store our results
ans_to_print = 0

# Defining the function for calculation
def Calculate(event):
  
    # getting the name of the button clicked
    button = event.widget.cget("text")

    # Referring the global values
    global key_matrix, inp, ans_to_print

    try:
        # Event containing a sqrt operation
        if button == u"\u221A":
            ans = float(inp.get())**(0.5)
            ans_to_print = str(ans)
            inp.set(str(ans))

        elif button == "c":  # Clear Button
            inp.set("")

        elif button == "!":  # Factorial
            def fact(n): return 1 if n == 0 else n*fact(n-1)
            inp.set(str(fact(int(inp.get()))))

        elif button == "<-":  # Backspace
            inp.set(inp.get()[:len(inp.get())-1])

        elif button == "=":  # Showing The Results
            # Calculating the mathematical exp. using eval
            ans_to_print = str(eval(inp.get()))
            inp.set(ans_to_print)

        # You may add many more operations

        else:
            # Displaying the digit pressed on screen
            inp.set(inp.get()+str(button))

    except:
        # In case invalid syntax given in expression
        inp.set("Wrong Operation")

        

# Creating the buttons using for loop

# Number of rows containing buttons
for i in range(len(key_matrix)):  
    # Number of columns  
    for j in range(len(key_matrix[i])):  

        # Creating and Adding the buttons to dictionary
        btn_dict["btn_"+str(key_matrix[i][j])] = Button(
          root, bd=1, text=str(key_matrix[i][j]), font=myFont)
        
        # Positioning buttons
        btn_dict["btn_"+str(key_matrix[i][j])].grid(
          row=i+1, column=j, padx=5, pady=5, ipadx=5, ipady=5)
        
        # Assigning an action to the buttons
        btn_dict["btn_"+str(key_matrix[i][j])].bind('<Button-1>', Calculate)

# Running the main loop
root.mainloop()