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README.md

Flask 🐍

What is flask?

  • A micro web framework written in Python
  • It is called microframework because it does not require particular tools or libraries.
  • It has no database abstraction layer, form validation, or any other components where pre-existing third-party libraries provide common functions.
  • Allows developers to build web applications easily
  • A lightweight WSGI web application framework

💡 Developed by Armin Ronacher, who led team of international Python enthusiasts called Poocco 💡

What is a web framework?

  • Represents a collection of libraries and modules that enable web application developers to write applications without worrying about low-level details such as protocol, thread management, etc.

What is a micro framework?

  • Refers to minimalistic web application frameworks
  • Lacks most functionality which is common to expect in full-fledged web application framework (accounts, authentication, authorisation, etc)

Boilerplate code example

from flask import Flask
app = Flask(__name__)

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

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

Running flask in dev environment

bash-3.2$ export FLASK_ENV=development 
bash-3.2$ flask run
 * Serving Flask app "hello" (lazy loading)
 * Environment: development
 * Debug mode: on
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
 * Restarting with stat
 * Debugger is active!
 * Debugger PIN: 891-424-380

If you already have a process bound to the default port (5000), locate the process:

$ ps -fA | grep python
501 81651 12648 0 9:53PM ttys000 0:00.00 grep python

Stop the server by sending it a signal (the second number - process number)

kill 81651

or:

Run the server on a different* port, by specifying the alternative port on the command line:

$ python -m SimpleHTTPServer 8910
Serving HTTP on 0.0.0.0 port 8910

Then access the server as http://localhost:8910; where 8910 can be any number from 1024 and up, provided the port is not already taken.

Pros and Cons of Flask

Pros Cons
Easy to get started Extremely limited, you have to build almost everything that you want to do in Flask
Very customisable No database support, you have to write all your custom SQL statements and create objects and turn them back into database data.
Web Server Gateway Interface (WSGI) compatible

Terminology

Model View Controller (MVC)

  • A software design pattern used for developing user interfaces that divides the related program logic into three interconnected elements, Model, View and Controller.
  • The MVC model or 'pattern' is used for developing modern user interfaces.
  • Each architecture component is built to handle specific development aspect of an application
  • MVC separates the business logic and presentation layer from each other.

mvc_image

  • Model - Includes all data and its related logic (a way for talking about data)
  • View - Presents data and its related logic (a way for talking about user interfaces) MVC is HTML, CSS and some special syntax.
  • Controller - An interface between Model and View components (a way for talking about program logic) aka the request handler

When a user enters a URL in the browser, it goes to the webserver and routed to a controller. A controller executes related view and models for that request and creates the response and sends it back to the browser.

Flask MVC Structure: What?

  • A popular architecture for designing applications that have a user interface
  • MVC is a collection of software design patterns that provide a vocabulary for designing your application.

End Point

  • Any device that is physically an end point on a network
  • One end of a communication channel

WSGI (Web Server Gateway Interface)

Frameworks Servers
Flask Gunicorn
Django uWSGI
  • WSGI is a protocol for Python applications in order to serve websites in a uniform manner.
  • Examples of Python frameworks include Flask or Django
  • Examples of servers include Gunicorn and uWSGI
  • If we have a Python framework that wants to serve webpages, if it follows the WSGI format, that means that any Python framework you choose can work with any compatible WSGI server.
  • Flask and Django by default implement those, same as Gunicorn and uWSGI

Flask Projects