Flask-Basic more

Sure! Here are some notes for getting started with Flask, a lightweight web framework for Python:

Flask Basics

1. Introduction to Flask

Flask is a micro web framework for Python based on Werkzeug and Jinja2.
It is lightweight and designed with simplicity in mind, making it easy to start with web development in Python.

2. Installation

Install Flask using pip:
```
pip install Flask
```

3. Hello World Example

Create a simple Flask application:

from flask import Flask

app = Flask(__name__)

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

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

Run the application:
```
python app.py
```

4. Routing

Define routes to handle different URLs:

@app.route('/home')
def home():
    return 'Welcome to the Home Page'

@app.route('/about')
def about():
    return 'About Page'

5. Dynamic Routing

Use dynamic routing to capture parts of the URL:

@app.route('/user/<username>')
def show_user_profile(username):
    return f'User: {username}'

@app.route('/post/<int:post_id>')
def show_post(post_id):
    return f'Post ID: {post_id}'

Templates

1. Using Templates

Templates are used to render HTML pages. Flask uses Jinja2 as its template engine.

Create a templates folder and add HTML files.

<!-- templates/index.html -->
<!doctype html>
<html>
  <head><title>Hello</title></head>
  <body>
    <h1>Hello, {{ name }}!</h1>
  </body>
</html>

2. Rendering Templates

Render templates using the render_template function:

from flask import render_template

@app.route('/hello/<name>')
def hello(name):
    return render_template('index.html', name=name)

Forms and Request Handling

1. Handling Forms

Use the request object to handle form data:

<!-- templates/form.html -->
<form action="/submit" method="post">
  <input type="text" name="name">
  <input type="submit">
</form>

Handle form submission in the view:

from flask import request

@app.route('/submit', methods=['POST'])
def submit():
    name = request.form['name']
    return f'Hello, {name}!'

Static Files

1. Serving Static Files

Create a static folder for static files like CSS, JavaScript, and images.

Reference static files in templates:

<link rel="stylesheet" href="{{ url_for('static', filename='style.css') }}">

Database Integration

1. Using SQLite with Flask

Use SQLite with Flask through the sqlite3 module or Flask extensions like Flask-SQLAlchemy.

Simple SQLite integration:

import sqlite3
from flask import g

DATABASE = 'mydatabase.db'

def get_db():
    db = getattr(g, '_database', None)
    if db is None:
        db = g._database = sqlite3.connect(DATABASE)
    return db

@app.teardown_appcontext
def close_connection(exception):
    db = getattr(g, '_database', None)
    if db is not None:
        db.close()

2. Using Flask-SQLAlchemy

Install Flask-SQLAlchemy:
```
pip install Flask-SQLAlchemy
```

Configure and use SQLAlchemy:

from flask_sqlalchemy import SQLAlchemy

app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///mydatabase.db'
db = SQLAlchemy(app)

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)

db.create_all()

Flask Extensions

Flask has many extensions for adding functionality, such as authentication, forms, and more.
Some popular Flask extensions:
- Flask-WTF for forms
- Flask-Login for user authentication
- Flask-Migrate for database migrations

Example Project Structure

my_flask_app/
├── app.py
├── templates/
│   ├── index.html
│   └── form.html
├── static/
│   └── style.css
├── models.py
└── config.py

Running the Flask Application

Set the FLASK_APP environment variable and run the application:
```
export FLASK_APP=app.py
flask run
```

This should give you a good starting point for working with Flask. As you progress, you can explore more advanced features and best practices for building scalable and secure Flask applications.

jashasmani/Flask-Basic