This document provides an introduction to building web applications with the Flask framework in Python. It discusses why Flask is a good option, gives an overview of Python and its advantages as a language, and demonstrates basic Flask concepts like routing, templates, models, and deployment. The key steps shown include setting up a virtual environment, creating a basic "Hello World" app, using Jinja templates, the Flask-SQLAlchemy extension for databases, and deploying to platforms like Heroku.

1. Building Web
Applications With Flask:
For CS Students
By Jennifer Rubinovitz
@rubinovitz

2. Why Flask?
● lightweight
● python
● (relatively) easy to deploy

3. Python: as a language
●
●
●
●
Clear syntax
Object oriented
Great community and packages
Fast (enough). Compiles to C

4. Python: Hello World
print ‘hello world’
python 2.*
print(“hello world”)
python 3.*

5. Python: Recommended Resources
●
●
●
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Learn Python the Hard Way
Python Documentation
Codeacademy
Flask Documentation

6. Installing Python
Differs based on operating system
http://www.python.
org/getit/
Downloads:

7. Python Package Management
PIP:
Allows you to download python packages on
the fly:
http://www.pip-installer.org/en/latest/installing.html
pip install packagename==versionNumber

8. Virtualenv
Creates isolated python environments and
install an applications requirements
Command line
virtualenv venv
. venv/bin/activate
pip install -r requirements.
txt
requirements.txt
flask==0.10.1

9. Model-View-Controller(MVC)

10. Hello World: simple_server.py
import os
from flask import Flask, render_template
app = Flask(__name__)
@app.route('/')
def index():
return render_template("index.html")
if __name__ == '__main__':
app.run(debug=True, port=8000)

11. Routing: unique url rules
@app.route('/')
def index():
return 'Index Page'
@app.route('/hello')
def hello():
return 'Hello World'
Flask routing documentation

12. Routing: variable urls
@app.route('/user/<username>')
def show_user_profile(username):
# show the user profile for that user
return 'User %s' % username
@app.route('/post/<int:post_id>')
def show_post(post_id):
# show the post with the given id, the id is an integer
return 'Post %d' % post_id

13. Routing: HTTP
@app.route('/login', methods=['GET', 'POST'])
def login():
if request.method == 'POST':
do_the_login()
else:
show_the_login_form()

14. Templates: Jinga
{% extends "layout.html" %}
{% block body %}
<ul>
{% for user in users %}
<li><a href="{{ user.url }}">{{ user.username }}</a></li>
{% endfor %}
</ul>
{% endblock %}
Jinga Documentation

15. Models: classes
Models are abstractions of database tables
from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:////tmp/test.db'
db = SQLAlchemy(app)
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(80), unique=True)
email = db.Column(db.String(120), unique=True)
def __init__(self, username, email):
self.username = username
self.email = email

16. Models: operations
# create a user
jen = User(username=”jen”, email=”jen@email.
com”)
# save user to database
db.session.add(jen)
db.session.commit()
# retrieve user
jen =db.session.query.filter_by(username=”jen”).
first()

17. Favorite Flask Modules
● Flask-Sqlalchemy(for database interaction)
note: flask-sqlalchemy is a sqlalchemy wrapper for flask, and their syntax
differs. Make sure you use the correct documentation.
● Flask-Security (for user management)
● WTForms(for forms)

18. Deployment
● Heroku
● Appfog
● Or deploy on your own server

19. Questions?