Building a To-Do List Application in CLI Using Python

Introduction

In the journey of learning Python, one of the best ways to strengthen your programming skills is by building small, practical projects. These projects not only help you apply theoretical concepts but also give you hands-on experience in solving real-world problems. In this article, we will dive into Building a To-Do List Application in CLI Using Python. A command-line interface (CLI) To-Do List is a perfect beginner-friendly project that teaches you how to work with lists, loops, functions, and user input in Python.

By the end of this article, you will be able to build your own interactive To-Do List application that allows users to add, view, and delete tasks — all from the terminal. We will also walk through the sample code, break it down into understandable chunks, and showcase what the output looks like when you run the program.

Problem Statement

The problem we are solving is simple: Create a command-line To-Do List app that lets users add, view, and delete tasks during a session.

While this may sound basic, it actually covers some essential programming concepts, including:

List operations (adding, removing, displaying items)
Functions (organizing code into reusable blocks)
Loops and conditionals (controlling the flow of the program)
Error handling (ensuring the program doesn’t crash on invalid input)
User input handling (taking commands interactively)

What You’ll Learn

By creating this project, you’ll develop important Python skills such as:

Understanding list operations: adding tasks to a list, removing them, and iterating through the list.
Writing and organizing functions to make the code modular and easier to read.
Implementing loops to continuously show the menu until the user decides to exit.
Using conditionals to handle different user choices.
Handling user input gracefully, including invalid cases.
Building a CLI application that interacts with the user directly.

These are foundational skills that you will use in more advanced Python projects later on.

Step-by-Step Guide to Building the To-Do List

Step 1: Setting up the To-Do List

The first step is to create an empty list that will store all tasks. In Python, we can easily manage tasks using a list because it supports dynamic addition and removal of items.

todo_list = []

Here, todo_list is an empty list that will hold all the tasks we add.

Step 2: Displaying the Tasks

We want to give the user the ability to see what tasks have been added. For this, we will write a function called show_tasks().

def show_tasks():
    if not todo_list:
        print("No tasks yet.")
    else:
        for i, task in enumerate(todo_list, 1):
            print(f"{i}. {task}")

Explanation:

We first check if the list is empty using if not todo_list:. If true, we display “No tasks yet.”
If there are tasks, we use enumerate() to loop through the list and print each task with a number starting from 1.

Step 3: Adding a Task

Next, we allow the user to add tasks. For this, we define the add_task(task) function.

def add_task(task):
    todo_list.append(task)
    print("Task added.")

Explanation:

append() is used to add a task to the list.
A confirmation message “Task added.” is displayed after successfully adding.

Step 4: Deleting a Task

Users should also be able to delete tasks. For this, we will write the delete_task(index) function.

def delete_task(index):
    if 0 < index <= len(todo_list):
        removed = todo_list.pop(index - 1)
        print(f"Deleted: {removed}")
    else:
        print("Invalid task number.")

Explanation:

We check if the given index is valid (greater than 0 and less than or equal to the length of the list).
If valid, we use pop(index-1) to remove the task at that position.
We also print which task was deleted.
If the index is invalid, we display “Invalid task number.”

Step 5: Building the Menu Loop

Now that we have functions for viewing, adding, and deleting tasks, we need a menu system that continuously runs until the user exits.

while True:
    print("\n=== To-Do List ===")
    print("1. View Tasks")
    print("2. Add Task")
    print("3. Delete Task")
    print("4. Exit")

    choice = input("Choose an option (1-4): ")

    if choice == '1':
        show_tasks()
    elif choice == '2':
        task = input("Enter task: ")
        add_task(task)
    elif choice == '3':
        show_tasks()
        try:
            idx = int(input("Enter task number to delete: "))
            delete_task(idx)
        except ValueError:
            print("Please enter a valid number.")
    elif choice == '4':
        print("Goodbye!")
        break
    else:
        print("Invalid option.")

Explanation:

while True: keeps the program running until the user chooses to exit.
The menu options are displayed every time.
Based on user input, different functions are called.
If the user enters 4, the program prints “Goodbye!” and exits.
Invalid inputs are handled gracefully with an error message.

Complete Source Code

Here’s the full Python code for the project:

todo_list = []

def show_tasks():
    if not todo_list:
        print("No tasks yet.")
    else:
        for i, task in enumerate(todo_list, 1):
            print(f"{i}. {task}")

def add_task(task):
    todo_list.append(task)
    print("Task added.")

def delete_task(index):
    if 0 < index <= len(todo_list):
        removed = todo_list.pop(index - 1)
        print(f"Deleted: {removed}")
    else:
        print("Invalid task number.")

while True:
    print("\n=== To-Do List ===")
    print("1. View Tasks")
    print("2. Add Task")
    print("3. Delete Task")
    print("4. Exit")

    choice = input("Choose an option (1-4): ")

    if choice == '1':
        show_tasks()
    elif choice == '2':
        task = input("Enter task: ")
        add_task(task)
    elif choice == '3':
        show_tasks()
        try:
            idx = int(input("Enter task number to delete: "))
            delete_task(idx)
        except ValueError:
            print("Please enter a valid number.")
    elif choice == '4':
        print("Goodbye!")
        break
    else:
        print("Invalid option.")

Sample Interaction

Here’s how the program looks when you run it in the terminal:

=== To-Do List ===
1. View Tasks
2. Add Task
3. Delete Task
4. Exit
Choose an option (1-4): 2
Enter task: Learn Python
Task added.

=== To-Do List ===
1. View Tasks
2. Add Task
3. Delete Task
4. Exit
Choose an option (1-4): 1
1. Learn Python

=== To-Do List ===
1. View Tasks
2. Add Task
3. Delete Task
4. Exit
Choose an option (1-4): 2
Enter task: Practice Coding
Task added.

=== To-Do List ===
1. View Tasks
2. Add Task
3. Delete Task
4. Exit
Choose an option (1-4): 1
1. Learn Python
2. Practice Coding

=== To-Do List ===
1. View Tasks
2. Add Task
3. Delete Task
4. Exit
Choose an option (1-4): 3
1. Learn Python
2. Practice Coding
Enter task number to delete: 1
Deleted: Learn Python

=== To-Do List ===
1. View Tasks
2. Add Task
3. Delete Task
4. Exit
Choose an option (1-4): 1
1. Practice Coding

=== To-Do List ===
1. View Tasks
2. Add Task
3. Delete Task
4. Exit
Choose an option (1-4): 4
Goodbye!

This interaction demonstrates how you can add multiple tasks, view them, delete tasks by their number, and exit the application.

Exploring Key Learnings

This project may look simple, but it introduces you to the following important concepts:

Data Storage: Tasks are stored in a Python list, showing how lists can be used dynamically.
Functions and Code Structure: Functions make the program modular and reusable.
Input Validation: By checking for valid task numbers, the program avoids errors.
User Interaction: Running in a loop keeps the program interactive and user-friendly.
Practical Application: A To-Do List is something people use in real life, making this project relatable and useful.

With this foundation, you can extend the project further by adding features like:

Saving tasks to a file.
Marking tasks as completed.
Sorting tasks by priority.
Adding due dates.

By experimenting with these additions, you’ll take your Python learning to the next level.

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