Web Development With Flask

What is Flask?

A Python microframework for building web applications
Simple, easy to use
Can write APIs or process templates
Basically, we write server-side code with Python!

What are we doing?

This is a hackathon!
Our goal is to achieve a starting point for an application
After this workshop, you will have
- A basic understanding of Flask
- A running Flask application that can be extended
- Understanding of how to seek help with Flask

Requirements

Basic Python knowledge
No fear of running instructions on the command line
Sublime Text or another text editor
The desire to learn

A Basic Flask app

from flask import Flask
app = Flask("My Application")

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

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

simple.py

Running our app

# Set app in Windows

$ set FLASK_APP=simple.py

# Set app in MacOSX/Linux

$ export FLASK_APP=simple.py

# Run (both)

$ flask run

command line

result

Running our app

In Chrome

A More Complex Flask app

from flask import Flask
app = Flask("My Application")

@app.route("/user/<username>")
def hello(username):
    return "This is " + username + "'s page."

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

less_simple.py

Rendering Templates

from flask import Flask, render_template
app = Flask("My Template Application")

@app.route("/user/<username>")
def hello(username):
    return render_template('hello.html', username=username)

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

templates/hello.html

<!DOCTYPE html>
<html>
<head>
    <title>Hello {{username}}</title>
</head>
<body>
    <h1>Hello {{username}}</h1>
</body>
</html>

template_example.py

Reaching an API

from flask import Flask, render_template
import urllib2, json
app = Flask("My API Application")
API_ROOT = "http://api.icndb.com/"

@app.route("/norris/<category>")
def norris(category):
	url = API_ROOT + "jokes/random?limitTo=[" + category + "]"
	req = urllib2.urlopen(url)
	answer = json.loads(req.read())
	return render_template("api_info.html", **answer)

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

templates/api_info.html

<!DOCTYPE html>
<html>
<head>
	<title>API Data</title>
</head>
<body>
	<h5>Joke search: {{type}}</h5>
	<p>{{value.joke}}</p>
	<small>Categories: {{",".join(value.categories)}}
</body>
</html>

api_example.py

Limitations

Flask is a microframework, so it is best for small apps
We currently don't have users, authentication
Database support is possible, but not simple

Next Steps

You now have a few working examples
Work with these examples to build a more complex app
Need inspiration? Find a public API:
- https://github.com/toddmotto/public-apis
Use the Flask documentation!
- http://flask.pocoo.org/docs/

Get Hacking!

This presentation is available on GitHub
- https://github.com/jamiecounsell/flask-demo