saulugo / flask_architecture

My notes about Python Flask Application Architecture

#Flask Applications Architecture

A Flask App is structured the following way:

1. Application Instance: All Flask applications must create an application instance. The web server passes all requests it receives from clients to this object for handling using a protocol called Web Server Gateway Interface (WSGI)

The app instance is an object of the Class Flask. It is usually created as follow:

from flask import Flask
app = Flask(__name__)

2)Routes and View Functions: the client sends requests to the web server, who in turn sends them to the app instance. The app instance keeps a map of URLs (received from the web server - clients requests) and Python functions to be run for each URL. This association between a URL and a Python function is called a Route.

The Flask class has a decorator named app.route. This decorator is exposed by the app instance. Each route is defined in Flask using this decorator app.route.

Each route is declared as follow, using the app.route decoratore exposed by the application instance:

@app.route('/')
def index():
	return "<h1>Hello world!</h1>

The return of this function is called the response and it will be passed through the web server to the client browser.

The functions of each routes are called view functions.

When the URL has a variable part, for example you want a page in your app to be called by the user's username, you must use the following syntax in the route decorator:

@app.route('/user/<username>)
def user(name):
	return '<h1>Hello, %s!</h1>' % name

The the URL match the fix portion will call the view function (user(name)) and send the URL part enclosed in the angle brackets as a argument of the view function.

Also, the dynamic part of the URL, supports type definition. For example the route /user/int:id will accept only integers as the id.

Flask supports int, float and path class for the routes. The path type is a string but does not take the slashes as separators but as part of the dynamic content.

3)Server Startup: the application instance has the run method that launches Flask's integrated development web server.

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