Project 3: CLI-based To-do App in Python0%

Project 3: CLI-based To-do App in Python

Intermediate9 min read•Updated: 2026-10-01

Project 3: CLI-Based To-Do App in Python

In this project, we apply our cumulative understanding of Object-Oriented Architecture, SQLite Database Management, Datetime Arithmetic, and Defensive Error Handling to engineer a high-productivity Command-Line Task & To-Do Management Engine.

1. System Architecture & Capabilities

Our To-Do application manages task lifecycles stored in an embedded tasks.db SQLite database:

Visual Architecture Blueprint

+-----------------------------------------------------------------------------+
|                                tasks.db                                     |
|                                                                             |
|  id (PK) | title | priority (HIGH/MED/LOW) | status | due_date | created_at |
+-----------------------------------------------------------------------------+

Key Capabilities:

1
Full CRUD Lifecycle: Add, list, search, update status, and delete tasks.
2
Priority Hierarchy: Prioritizes tasks by HIGH, MEDIUM, and LOW.
3
Deadline Awareness: Compares task deadlines against current system time via the datetime module to flag OVERDUE tasks with visual alert tags.
4
Resilient CLI: Parameterized SQL queries safeguard against SQL injection, while comprehensive error trapping handles invalid date formats.

2. Complete Project Implementation

Visual Architecture & Process Flow

How data and code flow step-by-step

Flowchart

Step 1

def _get_connection

self

Step 2

sqlite3.Connection:

3. Sample Execution Simulation

1===== TERMINAL TASK & TO-DO MANAGER =====
21. View All Active Tasks
32. Add New Task
43. Mark Task Status (Pending / In-Progress / Completed)
54. View Completed Archive
65. Delete Task
76. Exit
8Select an option (1-6): 2
9 
10Enter task description: Prepare slide deck for board meeting
11Priority (HIGH / MEDIUM / LOW) [Default: MEDIUM]: HIGH
12Due Date (YYYY-MM-DD) or press Enter to skip: 2026-09-14
13Task #1 ('Prepare slide deck for board meeting') added successfully.
14 
15===== TERMINAL TASK & TO-DO MANAGER =====
16Select an option (1-6): 1
17 
18===========================================================================
19ID   | STATUS       | PRIORITY | DUE DATE             | TITLE
20---------------------------------------------------------------------------
211    | [PENDING]    | HIGH     | 2026-09-14           | Prepare slide deck for board meeting
22===========================================================================

⚠️ Common Intermediate Mistakes & Gotchas

1. Off-by-One Task Numbering

Users expect 1-based indexing for task lists (Task #1, #2), while Python lists use 0-based indexing. Always convert cleanly with idx = user_input - 1.

2. Unhandled Empty Task Lists

Guard against operations on empty task lists by displaying a friendly message ("No tasks found!") instead of raising an IndexError.

💻 Try It Yourself: Extension Challenge - Priority Sorting

Challenge

Extend the CLI To-Do App to support task priority levels (HIGH, MEDIUM, LOW) and display the active task list sorted by urgency.

Complete Solution

1PRIORITY_ORDER = {"HIGH": 1, "MEDIUM": 2, "LOW": 3}
2 
3def display_sorted_tasks(tasks):
4    sorted_tasks = sorted(tasks, key=lambda t: PRIORITY_ORDER.get(t["priority"].upper(), 99))
5    print(f"{'#':<3} | {'PRIORITY':<8} | {'TASK'}")
6    print("-" * 35)
7    for idx, t in enumerate(sorted_tasks, 1):
8        print(f"{idx:<3} | {t['priority']:<8} | {t['title']}")
9 
10tasks = [
11    {"title": "Buy groceries", "priority": "LOW"},
12    {"title": "Submit client report", "priority": "HIGH"},
13    {"title": "Review pull request", "priority": "MEDIUM"}
14]
15display_sorted_tasks(tasks)

Expected Output

1#   | PRIORITY | TASK
2-----------------------------------
31   | HIGH     | Submit client report
42   | MEDIUM   | Review pull request
53   | LOW      | Buy groceries

Interactive Quiz• Knowledge Check

Practice Quiz

Question 1

How does the SQLite table schema prevent arbitrary invalid values from being stored in the status column?

Question 2

How does the application detect that a task is OVERDUE?

Question 3

Which SQL clause allows custom hierarchical sorting (e.g. HIGH before MEDIUM before LOW)?

Question 4

What does cursor.lastrowid return after executing INSERT INTO tasks ...?

Question 5

Why is parameterized SQL syntax (VALUES (?, ?, ?)) used when adding new tasks?

🚀 What's Next?

In the next lesson, we will continue your intermediate Python journey with Library Management System (15: Capstone Project).

👉 Continue to Next Lesson: Library Management System →

Next Lesson

Library Management System

Continue learning with hands-on practice, examples, and exercises in the upcoming topic.

Related Lessons

Previous Lesson	Next Lesson
Project 2: API-based Dictionary App	Library Management System

Practice Quiz

Test your understanding of this lesson with 5 questions. Each question has one correct answer.

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Library Management System

Project 3: CLI-based To-do App in Python

Intermediate9 min read•Updated: 2026-10-01

Study Materials Cheatsheet

Project 3: CLI-Based To-Do App in Python

1. System Architecture & Capabilities

Our To-Do application manages task lifecycles stored in an embedded tasks.db SQLite database:

Visual Architecture Blueprint

+-----------------------------------------------------------------------------+
|                                tasks.db                                     |
|                                                                             |
|  id (PK) | title | priority (HIGH/MED/LOW) | status | due_date | created_at |
+-----------------------------------------------------------------------------+

Key Capabilities:

1
Full CRUD Lifecycle: Add, list, search, update status, and delete tasks.
2
Priority Hierarchy: Prioritizes tasks by HIGH, MEDIUM, and LOW.
3
Deadline Awareness: Compares task deadlines against current system time via the datetime module to flag OVERDUE tasks with visual alert tags.
4
Resilient CLI: Parameterized SQL queries safeguard against SQL injection, while comprehensive error trapping handles invalid date formats.

2. Complete Project Implementation

Visual Architecture & Process Flow

How data and code flow step-by-step

Flowchart

Step 1

def _get_connection

self

Step 2

sqlite3.Connection:

3. Sample Execution Simulation

1===== TERMINAL TASK & TO-DO MANAGER =====
21. View All Active Tasks
32. Add New Task
43. Mark Task Status (Pending / In-Progress / Completed)
54. View Completed Archive
65. Delete Task
76. Exit
8Select an option (1-6): 2
9 
10Enter task description: Prepare slide deck for board meeting
11Priority (HIGH / MEDIUM / LOW) [Default: MEDIUM]: HIGH
12Due Date (YYYY-MM-DD) or press Enter to skip: 2026-09-14
13Task #1 ('Prepare slide deck for board meeting') added successfully.
14 
15===== TERMINAL TASK & TO-DO MANAGER =====
16Select an option (1-6): 1
17 
18===========================================================================
19ID   | STATUS       | PRIORITY | DUE DATE             | TITLE
20---------------------------------------------------------------------------
211    | [PENDING]    | HIGH     | 2026-09-14           | Prepare slide deck for board meeting
22===========================================================================

⚠️ Common Intermediate Mistakes & Gotchas

1. Off-by-One Task Numbering

Users expect 1-based indexing for task lists (Task #1, #2), while Python lists use 0-based indexing. Always convert cleanly with idx = user_input - 1.

2. Unhandled Empty Task Lists

Guard against operations on empty task lists by displaying a friendly message ("No tasks found!") instead of raising an IndexError.

💻 Try It Yourself: Extension Challenge - Priority Sorting

Challenge

Extend the CLI To-Do App to support task priority levels (HIGH, MEDIUM, LOW) and display the active task list sorted by urgency.

Complete Solution

1PRIORITY_ORDER = {"HIGH": 1, "MEDIUM": 2, "LOW": 3}
2 
3def display_sorted_tasks(tasks):
4    sorted_tasks = sorted(tasks, key=lambda t: PRIORITY_ORDER.get(t["priority"].upper(), 99))
5    print(f"{'#':<3} | {'PRIORITY':<8} | {'TASK'}")
6    print("-" * 35)
7    for idx, t in enumerate(sorted_tasks, 1):
8        print(f"{idx:<3} | {t['priority']:<8} | {t['title']}")
9 
10tasks = [
11    {"title": "Buy groceries", "priority": "LOW"},
12    {"title": "Submit client report", "priority": "HIGH"},
13    {"title": "Review pull request", "priority": "MEDIUM"}
14]
15display_sorted_tasks(tasks)

Expected Output

1#   | PRIORITY | TASK
2-----------------------------------
31   | HIGH     | Submit client report
42   | MEDIUM   | Review pull request
53   | LOW      | Buy groceries

Interactive Quiz• Knowledge Check

Practice Quiz

Question 1

How does the SQLite table schema prevent arbitrary invalid values from being stored in the status column?

Question 2

How does the application detect that a task is OVERDUE?

Question 3

Which SQL clause allows custom hierarchical sorting (e.g. HIGH before MEDIUM before LOW)?

Question 4

What does cursor.lastrowid return after executing INSERT INTO tasks ...?

Question 5

Why is parameterized SQL syntax (VALUES (?, ?, ?)) used when adding new tasks?

🚀 What's Next?

In the next lesson, we will continue your intermediate Python journey with Library Management System (15: Capstone Project).

👉 Continue to Next Lesson: Library Management System →

Next Lesson

Library Management System

Continue learning with hands-on practice, examples, and exercises in the upcoming topic.

Related Lessons

Previous Lesson	Next Lesson
Project 2: API-based Dictionary App	Library Management System

Practice Quiz

Test your understanding of this lesson with 5 questions. Each question has one correct answer.

Previous Next