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Introduction to Web Development with Flask

Introduction to Web Development with Flask

Certainly, Flask is a popular Python web framework that makes it easy to build web applications. Here's an introduction to web development using Flask:

1. What is Flask?

  • Flask is a lightweight and flexible micro web framework for Python.
  • It's designed to be simple and easy to use, making it a great choice for small to medium-sized web applications.

Getting Started with Flask:

1. Installation:

  • Install Flask using pip install Flask.

2. Hello World Example:

  • Create a basic Flask app with a "Hello, World!" route.

 

from flask import Flask

app = Flask(__name__)

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

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

 

 

Run the app with python app.py and access it in a web browser at http://localhost:5000.

 

Routing and Views:

1. Routing:

  • Define routes using the @app.route() decorator.
  • Routes map URLs to functions that handle requests.

2. Views:

  • View functions return content that's displayed in the user's browser.
  • They can return HTML, templates, or JSON data.

Templates with Jinja2:

1. Jinja2 Templates:

  • Flask uses the Jinja2 templating engine to generate dynamic HTML.

 

2. Rendering Templates:

  • Render templates using the render_template() function.

 

from flask import Flask, render_template

app = Flask(__name__)

@app.route("/")
def index():
    return render_template("index.html")

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

 

 

Handling Forms:

1. Forms:

  • Use HTML forms to collect data from users.

2. Handling Form Submissions:

  • Handle form submissions using POST requests.

 

from flask import Flask, render_template, request

app = Flask(__name__)

@app.route("/", methods=["GET", "POST"])
def index():
    if request.method == "POST":
        name = request.form.get("name")
        return f"Hello, {name}!"
    return render_template("form.html")

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

 

 

Static Files:

  • Place static files (CSS, JavaScript, images) in a directory named static within your Flask app's directory.
  • Use the url_for() function to generate URLs for static files.

Example:

Here's a simple example with routes, templates, and handling form submissions:

Create a directory structure:

 

myapp/
  ├─ app.py
  ├─ templates/
  │    └─ index.html
  └─ static/
    

 

 

app.py:

from flask import Flask, render_template, request

app = Flask(__name__)

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

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

 

 

templates/index.html:

      <!DOCTYPE html>
<html>
<head>
    <title>Flask App</title>
</head>
<body>
    <form method="post">
        <label for="name">Name:</label>
        <input type="text" id="name" name="name">
        <button type="submit">Submit</button>
    </form>
</body>
</html>

 

 

 

templates/greeting.html:

<!DOCTYPE html>
<html>
<head>
    <title>Greeting</title>
</head>
<body>
    <h1>Hello, widget_132594007733!</h1>
</body>
</html>

 

 

This example demonstrates a simple Flask app that takes a name input through a form, processes it, and displays a greeting using a template.