Creating a Calculator with Python's Tkinter: A GUI Application Exercise

Introduction
Prerequisites
Setup and Software
Creating the Calculator GUI
Creating the Calculator Functionality
Running the Calculator
Recap and Conclusion

Introduction

In this tutorial, we will create a simple calculator GUI (Graphical User Interface) using Python’s Tkinter library. This exercise will help you understand how to build interactive applications with a graphical interface in Python. By the end of this tutorial, you will have a working calculator that can perform basic arithmetic operations.

Prerequisites

Before starting this tutorial, you should have a basic understanding of Python programming language concepts such as variables, functions, and conditionals. Familiarity with GUI concepts will also be helpful but not necessary.

Setup and Software

To create the calculator GUI, we will be using the Tkinter library, which is included in most Python installations by default. There is no need for any additional installation.

Creating the Calculator GUI

First, let’s import the necessary modules by adding the following code at the beginning of your Python script:
```
 from tkinter import *
```
The tkinter module provides the classes and functions that we need to build our GUI.
Next, let’s create the main window of our calculator using the Tk() class:
```
 window = Tk()
 window.title("Calculator")
```
We create a new instance of the Tk class and set a title for the window.
Now, let’s create the display area of our calculator:
```
 display = Entry(window, width=40, borderwidth=5)
 display.grid(row=0, column=0, columnspan=3, padx=10, pady=10)
```
We create an Entry widget, which is a box where the user can enter input, and set its width to 40 characters. We then position the widget using the grid layout manager.

Next, let’s create the buttons for the digits and operators:

 button_1 = Button(window, text="1", padx=20, pady=10)
 button_2 = Button(window, text="2", padx=20, pady=10)
 button_3 = Button(window, text="3", padx=20, pady=10)
 # ... create buttons for other digits and operators

We create instances of the Button class, specify the button text, and set the padding using the padx and pady parameters.

Now, let’s position the buttons using the grid layout manager:

 button_1.grid(row=1, column=0)
 button_2.grid(row=1, column=1)
 button_3.grid(row=1, column=2)
 # ... position other buttons accordingly

We specify the row and column numbers to define the position of each button.

Finally, let’s add functionality to the buttons:
```
 def button_click():
     # code to handle button click
	
 button_1 = Button(window, text="1", padx=20, pady=10, command=button_click)
```
We define a function button_click that will be called when a button is clicked. We then associate this function with each button using the command parameter.

Creating the Calculator Functionality

First, let’s define a variable to store the input expression:
```
 expression = ""
```
This variable will store the arithmetic expression entered by the user.
Now, let’s define the button_click function to handle button clicks:
```
 def button_click(num):
     global expression
     expression += str(num)
     display.delete(0, END)
     display.insert(0, expression)
```
We update the expression variable with the clicked button’s number, update the display widget to show the current expression, and add the clicked number to the end of the expression.
Next, let’s define a function to handle the equal button:
```
 def equal_click():
     global expression
     result = eval(expression)
     display.delete(0, END)
     display.insert(0, result)
     expression = ""
```
We evaluate the expression using the eval function, which interprets the given string as a Python expression. We then update the display widget with the result and clear the expression variable.
Lastly, let’s define a function to clear the display and reset the expression:
```
 def clear_click():
     global expression
     display.delete(0, END)
     expression = ""
```
This function simply clears the display widget and resets the expression variable.

Running the Calculator

To run the calculator, add the following code at the end of your script:
```
 window.mainloop()
```
This code starts the main event loop, which listens for user actions such as button clicks.
Save your script with a .py extension and run it using your Python interpreter.
You should now see the calculator window with all the buttons and the display area. You can click the buttons to enter numbers and perform calculations.

Recap and Conclusion

In this tutorial, we have learned how to create a simple calculator GUI using Python’s Tkinter library. We covered the steps for creating the calculator interface, adding functionality to the buttons, and running the calculator application. By following this tutorial, you should now be able to build basic GUI applications in Python and understand the fundamentals of using Tkinter.

Throughout the tutorial, we discussed important concepts such as creating widgets, positioning them using the grid layout manager, handling button clicks, and evaluating expressions. We also learned how to update the display area and clear the calculator’s state.

Remember that this calculator is a basic implementation and can be further enhanced with advanced features such as additional operations, error handling, and better user experience. Use this tutorial as a starting point to explore and experiment with more advanced concepts in GUI programming with Tkinter.

Congratulations on completing this tutorial! Happy coding!

Published: 25 April 2022