1. Introduction

This tutorial aims to guide you in understanding the basic structure of a Flask application. Flask is a popular lightweight web framework in Python that comes in handy when developing web applications. By the end of this tutorial, you will learn how to structure your Flask application effectively, and this knowledge will aid in maintaining and scaling your projects with ease.

Prerequisites: Basic knowledge of Python and web development concepts.

2. Step-by-Step Guide

A Flask application typically consists of the following files and directories:

• app.py: This is the main entry point of your application where you'll define routes and views.
• templates/: This directory contains all your Jinja2 templates which are used to generate HTML from your views and models.
• static/: This is where all your static files like CSS, JavaScript, images go.
• models.py: (optional) If you're using a database, models are defined here.
• forms.py: (optional) If you're using Flask-WTF or similar library for forms, you define your forms here.

Best practices and tips:

• Always separate your application into logical components. For instance, separate models, forms, and routes into different modules.
• Use the templates/ and static/ directories for HTML and static files respectively.
• Always manage your dependencies with a requirements.txt file.

3. Code Examples

Consider the following example of a basic Flask application:

# app.py
from flask import Flask, render_template

app = Flask(__name__)

@app.route('/')
def home():
    return render_template('home.html')

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

In the above code snippet:

• We first import the Flask module and create a Flask web server from the Flask module.
• @app.route('/') is a decorator in Flask, which tells the application to call the associated function when the specified URL is visited.
• def home(): defines a function that returns "home.html" file to the user's browser when a request comes from the browser.
• if __name__ == '__main__': ensures the server only runs if the script is executed directly from the Python interpreter and not used as an imported module.

Expected output: When you navigate to http://localhost:5000/, you should see the contents of "home.html".

4. Summary

In this tutorial, we covered the basic structure of a Flask application. You've learned about the main components of a Flask application and their purpose. You now know how to structure your Flask application effectively.

For further learning, you can explore Flask documentation, tutorials, and other resources available online.

5. Practice Exercises

1. Create a new route /about and a new function about() that returns an 'about.html' page.
2. Create a route /user/<username> that takes username as input and returns a 'Hello, username' message.
3. Add a static CSS file to your application and use it to style your home page.

Solutions

1. To create a new route and function:

@app.route('/about')
def about():
    return render_template('about.html')

1. To create a route with variable parts:

@app.route('/user/<username>')
def profile(username):
    return 'Hello, %s!' % username

1. Add a file style.css in static/ directory. You can use it in your HTML as follows:

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

Remember to keep practicing and building projects with Flask to get the hang of it!