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<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8"/>
  <meta name="viewport" content="width=device-width, initial-scale=1"/>
  <meta name="description"
        content="Chapter 21 of Python Zero to Hero: build web apps and APIs with Flask and FastAPI—routing, templates, request handling, and deployment."/>
  <meta name="keywords"
        content="Python, web development, Flask, FastAPI, routing, templates, Jinja2, dependency injection, deployment"/>
  <meta name="author" content="Luca Bocaletto"/>
  <title>Chapter 21 – Web Development with Flask &amp; FastAPI | Python Zero to Hero</title>

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    <header class="my-4">
      <h1 class="display-6">Chapter 21: Web Development with Flask &amp; FastAPI</h1>
      <p class="text-muted">
        Learn how to create web applications and RESTful APIs using Flask and FastAPI, from routing to templating and deployment.
      </p>
      <a href="src/chapter21.py" download class="btn btn-outline-primary btn-sm btn-py">
        Download <code>chapter21.py</code>
      </a>
      <hr>
    </header>

    <section id="objectives" class="mb-5">
      <h2>Objectives</h2>
      <ul>
        <li>Set up a basic Flask app: routes, views, templates.</li>
        <li>Handle HTTP methods, query params and form data.</li>
        <li>Build REST APIs with FastAPI: path &amp; body parameters, validation.</li>
        <li>Use Jinja2 for dynamic HTML templates.</li>
        <li>Deploy a Flask/FastAPI app with Uvicorn or Gunicorn.</li>
      </ul>
    </section>

    <section id="flask-basics" class="mb-5">
      <h2>1. Flask Basics</h2>
      <pre><code class="python">from flask import Flask, request, render_template

app = Flask(__name__)

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

@app.route("/greet/<name>")
def greet(name):
    return f"Welcome, {name}!"

@app.route("/submit", methods=["GET","POST"])
def submit():
    if request.method == "POST":
        data = request.form.get("data")
        return render_template("result.html", data=data)
    return render_template("form.html")

if __name__ == "__main__":
    app.run(debug=True)</code></pre>
    <p>Templates folder structure:</p>
    <pre><code class="bash">templates/
├── form.html
└── result.html</code></pre>
    <p>form.html example:</p>
    <pre><code class="html">&lt;form method="post"&gt;
  &lt;input name="data" /&gt;
  &lt;button&gt;Send&lt;/button&gt;
&lt;/form&gt;</code></pre>
    <p>result.html example:</p>
    <pre><code class="html">&lt;p&gt;You submitted: {{ data }}&lt;/p&gt;</code></pre>
    <hr>
  </section>

    <section id="fastapi-basics" class="mb-5">
      <h2>2. FastAPI Basics</h2>
      <pre><code class="python">from fastapi import FastAPI
from pydantic import BaseModel

class Item(BaseModel):
    name: str
    price: float

app = FastAPI()

@app.get("/items/{item_id}")
def read_item(item_id: int, q: str | None = None):
    return {"item_id": item_id, "q": q}

@app.post("/items/")
def create_item(item: Item):
    return {"message": "Created", "item": item}

# run with: uvicorn src.chapter21:app --reload</code></pre>
    <hr>
  </section>

    <section id="deployment" class="mb-5">
      <h2>3. Deployment</h2>
      <pre><code class="bash"># gunicorn for Flask
gunicorn --bind 0.0.0.0:8000 wsgi:app

# uvicorn for FastAPI
uvicorn src.chapter21:app --host 0.0.0.0 --port 8000</code></pre>
    </section>

    <section id="exercises" class="mb-5">
      <h2>Exercises</h2>
      <ol>
        <li>Create a Flask “to-do” app with add/delete tasks stored in memory.</li>
        <li>Write a FastAPI endpoint that validates a JSON payload of user data.</li>
        <li>Use Jinja2 template inheritance to build a common layout for Flask pages.</li>
        <li>Containerize your Flask/FastAPI app with Docker and run locally.</li>
      </ol>
    </section>

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