AI and the Web: Task 2 – Build a search engine.

Here are some tips for the task:

  1. Concerning Flask

Summary of Flask

Flask is a lightweight web framework for Python designed to build web applications, APIs, and microservices. It is a micro-framework, meaning it provides the essentials for web development while remaining unopinionated and highly extensible, leaving many architectural decisions to the developer. Flask is ideal for developers who want a simple, flexible solution that can be scaled up with add-ons.

Main Design Principles

  1. Minimalism: Flask includes only the core functionality needed for web development, such as routing, request handling, and templating.
  2. Flexibility: It allows developers to choose their tools, libraries, and extensions.
  3. Simplicity: Flask has a low learning curve and provides clear, Pythonic APIs.
  4. Extensibility: Developers can add additional functionality via extensions like Flask-SQLAlchemy for databases or Flask-WTF for forms.
  5. Lightweight: It doesn’t enforce a specific project structure, leaving developers free to organize their applications however they like.

How Flask Applications Differ

Flask Applications

Flask applications handle HTTP requests, respond to them, and run on a web server. They serve content to clients (e.g., browsers or apps) via endpoints defined in routes.

Example Flask Application:

from flask import Flask

app = Flask(__name__)

@app.route("/")
def hello_world():
    return "Hello, World!"

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

Key Points:

  • Runs in a web server context.
  • Users access it via a URL (e.g., http://localhost:5000/).
  • Uses @app.route() to define routes (URLs) and their corresponding handlers.

Ordinary Python Applications

Ordinary Python applications run as scripts or programs, typically interacting with files, databases, or the command line.

Key Points:

  • Runs in a terminal/console environment.
  • Outputs directly to the console.
  • Not designed for handling HTTP requests.

Python Notebooks

Python notebooks, such as Jupyter, are interactive tools for data analysis, visualization, and teaching. They are often used for running Python code in small, testable cells.

Example Jupyter Notebook Cell:

# Hello, World in a Notebook
print("Hello, World!")

Key Points:

  • Interactive environment for exploratory work.
  • Outputs appear inline beneath the code cell.
  • Primarily for data science, plotting, and learning rather than web services.

Why Use Flask?

Flask is the go-to choice when you need to serve dynamic content, build a user interface for a Python application, or expose functionality to other applications via APIs. It excels at creating web-facing Python programs, which is distinct from the typical standalone or notebook-based workflows in Python.

4-Step Guide to Designing Flask Applications

Step 1: Plan Your Application

Before writing any code, clearly define your application’s purpose, features, and structure.

  • Identify Goals: Determine what the app should do (e.g., serve dynamic content, expose an API, or handle user authentication).
  • Plan Routes: Decide what URLs will be used and what functionality each will handle (e.g., /, /login, /api/data).
  • Define Data Models: If your app requires persistent data, design your database schema (e.g., tables, fields, relationships).
  • Plan the Frontend (if applicable): Decide on static files (CSS, JavaScript) or templating engines (e.g., Jinja2, the default for Flask).

Step 2: Set Up Your Flask Environment

Prepare the development environment and establish the basic structure of your Flask app.

Install Flask:

pip install flask

Set Up the Project Structure: Organize your app files for scalability:

my_flask_app/
├── app.py               # Main entry point for the app
├── static/              # Static files (CSS, JS, images)
├── templates/           # HTML templates
├── models.py            # Database models (if any)
├── forms.py             # Forms (if using Flask-WTF)
└── requirements.txt     # Dependencies for the app

Initialize Flask App: Start with a basic structure:

from flask import Flask

app = Flask(__name__)

@app.route('/')
def home():
    return "Hello, Flask!"

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

Step 3: Implement Core Functionality

Build out the app’s core features using Flask’s routing, templating, and optional extensions.

  • Define Routes: Use @app.route to map URLs to functions:
@app.route('/welcome')
def welcome():
    return "Welcome to my Flask app!"

Use Templating: Serve dynamic HTML with Jinja2:

<!-- templates/home.html -->
<!DOCTYPE html>
<html>
<head>
    <title>Home</title>
</head>
<body>
    <h1>{{ message }}</h1>
</body>
</html>
from flask import render_template

@app.route('/')
def home():
    return render_template('home.html', message="Hello from Flask!")
  • Add Extensions: Extend functionality (e.g., databases with Flask-SQLAlchemy, forms with Flask-WTF).

Step 4: Test, Debug, and Deploy

Ensure your application runs smoothly and is ready for production.

  • Test Locally:
    • Run the app in development mode (debug=True) to catch errors.
    • Use tools like Postman or curl to test APIs.
  • Handle Errors: Define custom error pages:
@app.errorhandler(404)
def not_found(e):
    return "Page not found!", 404

Deploy: Deploy to a production server (e.g., Gunicorn, uWSGI) or hosting service (e.g., Heroku, AWS, Azure).

Pro Tips

  • Keep It Modular: Break large apps into blueprints for better scalability.
  • Secure the App: Protect against common vulnerabilities (e.g., CSRF, XSS, SQL injection).
  • Document Your API: If building an API, use tools like Swagger for documentation.
  • Use Version Control: Keep your code under version control (e.g., Git).

By following this 4-step process, you’ll create a Flask application that is structured, maintainable, and ready for production.

High-Level Summary of HTTP

HTTP (Hypertext Transfer Protocol) is the foundational communication protocol of the World Wide Web, enabling the exchange of data between clients (e.g., web browsers) and servers. It is a request-response protocol that defines how data is formatted and transmitted and how servers and browsers should respond to various commands.

Key Features

  1. Request-Response Model:
    • A client sends a request (e.g., for a webpage).
    • A server processes the request and sends back a response (e.g., HTML content, JSON data, or an error).
  2. Stateless:
    • Each HTTP request is independent; the server does not retain any information about previous requests. (State can be managed via cookies, sessions, or tokens.)
  3. Text-Based Protocol:
    • Requests and responses are human-readable text, making it simple to debug and understand.
  4. Resource-Oriented:
    • HTTP operates around resources (e.g., webpages, files, APIs), each identified by a unique URL (Uniform Resource Locator).

HTTP Request Components

An HTTP request consists of:

  1. Method: Indicates the desired action (e.g., GET, POST, PUT, DELETE).
  2. URL: Specifies the resource being requested.
  3. Headers: Contain metadata (e.g., authentication, content type, caching).
  4. Body (Optional): Included in methods like POST to send data to the server (e.g., form data, JSON).

HTTP Response Components

An HTTP response consists of:

  1. Status Code: Indicates the outcome of the request (e.g., 200 OK, 404 Not Found, 500 Internal Server Error).
  2. Headers: Provide metadata (e.g., content type, cache control).
  3. Body: Contains the actual resource or response data (e.g., HTML, JSON, image).

Common HTTP Methods

  • GET: Retrieve a resource.
  • POST: Send data to the server (e.g., form submission, API calls).
  • PUT: Update or replace an existing resource.
  • DELETE: Remove a resource.
  • PATCH: Partially update a resource.
  • OPTIONS: Check which methods are supported for a resource.

HTTP Versions

  1. HTTP/1.1: The most widely used version, supporting persistent connections and chunked transfers.
  2. HTTP/2: Introduced multiplexing, header compression, and improved performance.
  3. HTTP/3: Uses QUIC (UDP-based protocol) for faster and more reliable connections.

Secure HTTP (HTTPS)

  • Adds encryption via SSL/TLS to HTTP, ensuring data is securely transmitted and preventing eavesdropping or tampering.
  • HTTPS is essential for modern websites, especially those handling sensitive information (e.g., passwords, payment data).

HTTP in Action

A typical web interaction involves:

  1. Client: A browser requests a webpage (HTTP GET request).
  2. Server: Responds with the HTML content.
  3. Client: Loads additional resources (e.g., images, CSS, JS) via subsequent HTTP requests.

HTTP is the backbone of online communication, enabling the seamless flow of data that powers websites, APIs, and modern web applications.

High-Level Summary of HTML

HTML (HyperText Markup Language) is the standard language used to create and structure the content of web pages. It provides the foundational framework for displaying text, images, links, and multimedia on the web. HTML is not a programming language but a markup language, meaning it uses tags to annotate and define the structure of a document.

Key Features

  1. Structure: HTML provides a way to organize content into a meaningful hierarchy (e.g., headings, paragraphs, sections).
  2. Semantics: Uses descriptive tags (e.g., <header>, <footer>, <article>) to give content meaning and improve accessibility.
  3. Hypertext: Facilitates linking between pages and resources using <a> tags.
  4. Media Integration: Allows embedding of images, videos, and audio.
  5. Dynamic Interaction: Works in conjunction with CSS (styling) and JavaScript (interactivity) to create modern web applications.

HTML Document Structure

An HTML document has a standardized structure:

<!DOCTYPE html>
<html>
  <head>
    <title>Page Title</title>
    <meta charset="UTF-8">
  </head>
  <body>
    <h1>Welcome to My Website</h1>
    <p>This is a paragraph of text.</p>
    <a href="https://example.com">Visit Example</a>
  </body>
</html>

Key Components:

  1. <!DOCTYPE html>: Declares the document as HTML5.
  2. <html>: Root element of the document.
  3. <head>: Contains metadata (e.g., title, styles, character encoding).
  4. <body>: Contains the visible content of the webpage.

Common HTML Tags

  • Content Tags:
    • <h1> ... <h6>: Headings.
    • <p>: Paragraphs.
    • <ul> / <ol>: Lists (unordered and ordered).
    • <a href="URL">: Hyperlinks.
    • <img src="URL">: Images.
    • <table>: Tables.
  • Semantic Tags:
    • <header>: Page header.
    • <footer>: Page footer.
    • <article>: Self-contained content.
    • <section>: Thematic grouping of content.
  • Media Tags:
    • <audio>: Embed audio.
    • <video>: Embed video.
    • <iframe>: Embed other web pages.

HTML Evolution

  • HTML4: Widely used for many years; lacked semantic richness.
  • HTML5: Introduced semantic elements, multimedia support, and APIs for modern web development.

HTML in the Web Ecosystem

  • HTML: Defines the structure and content of the webpage.
  • CSS: Styles and formats the HTML content.
  • JavaScript: Adds interactivity and dynamic behavior.

Together, these technologies form the core of the web, with HTML serving as the backbone for organizing and presenting content in browsers.