OIM3640 - Problem Solving and Software Design

2025 Spring

Session 20 (4/08)

Today's Agenda

• Welcome/News/Announcements
• Debugging
• Introduction to Web Application - Flask

Welcome/News/Announcements

• Assignments/Project:
  • Assignment 3 (Web App): will be posted next class
  • Project Teaming: anyone not in a team yet?
  • Project Proposal: due 4/12, Saturday
• Communications
  • Meet with me in person during office hours at least once this semester.
  • Email - specify course # in subject title, e.g., "OIM3640: GitHub settings"
  • Use Slack/GitHub when asking code-related questions
• Questions?

What we have learned so far...

• Variables, Expressions, Statements
• Types: int, float, string, boolean, Nonetype, string, list, dictionary, tuple, set
• Functions
• Conditional Statements
• Iterations
• Pseudo-code
• Error Handling
• APIs and Automation

Debugging

• Debugging (from Think Python 2)
• Debugging (from Think Python 3)
• "My code isn't working :-("

Q&A

• Questions from exercises, quizzes, assignments.
• Issues on GitHub
• Any question today?

Introduction to Web Application - Flask

• What is Flask?
  • Flask is a micro web framework written in Python, used for building web applications, APIs, and microservices.
• Flask vs. Django?
  • Flask is simpler and more lightweight, great for small/medium-sized projects.
• Popular companies/websites using Flask:
  • Built With Flask: Pinterest, Zillow, Twilio, Patreon
  • In Tech Stack: Reddit, LinkedIn, Netflix, Lyft, Airbnb, ...

Flask - Routing

• What is routing in Flask?
  • It refers to the way in which HTTP requests are handled by a Flask app.
  • Examples:
    • https://www.MyTiktok.com/new
    • https://www.MyTiktok.com/1
    • https://www.MyTiktok.com/1/edit
• How does routing work in Flask?
  • Flask routes are defined using the @app.route() decorator.
  • The decorator is used to associate a URL endpoint with a view function.
  • When a user visits the URL associated with a route, Flask invokes the view function, which generates a response to send back to the user.

Quick Tutorial on Flask

• Installation

  > python -m pip install flask # Windows users
  > python3 -m pip install flask  # macOS/Linux users
  

• Creating our first Flask application
  • Create a project/folder, helloflask
  • Create a file named app.py
  • Copy code of "A Minimal Application" from Flask Quickstart
  • Turn on Debug Mode

    if __name__ == "__main__":
        app.run(debug=True)
    

Flask Resources

• Flask Quickstart
• Flask Tutorial in Visual Studio Code
• The Flask Mega-Tutorial, Part I: Hello, World!
• Flask Web App Demo
• YouTube - HTML for Flask