Start with Flask - Speaker Deck

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Christian Barra @christianbarra www.chrisbarra.me 1 Meetup Python Milan - 21/10/2014 Start with Flask

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WHAT IS FLASK ? 2

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• Flask is a “micro” framework • micro means that Flask keep the core simple but extensible • Flask won’t make many decisions for you, such as what database to use 3

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BASICALLY. 4

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• Werkzeug • Jinja2 • Others small things • No orm • No form • Only extensions 5

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FLASK IS FUN. 6

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7 from flask import Flask # Import Flask class app = Flask(__name__) # Create a new Flask instance @app.route(“/“) # Flask routing system def index(): # Your view return "Hello World” if __name__ == "__main__": app.run() # Run development server

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8 $ pip install flask $ python hello.py * Running on http://localhost:5000/

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RESPONSE OBJECT. 9

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from flask import Flask, jsonify app = Flask(__name__) @app.route("/") def index(): msg = {"type": False, "code": "Something went wrong"} # Return a json object with 500 status code return jsonify(msg), 500 if __name__ == "__main__": app.run() 10

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REQUEST OBJECT. 11

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12 from flask import Flask, request app = Flask(__name__) @app.route("/", methods=[‘POST']) # You can specific methods for every view def index(): # create a dict with request data data = request.json user = request.json[‘user’] … … … return "I got your data !” if __name__ == "__main__": app.run()

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METHOD VIEW. 13

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14 from flask.views import MethodView class UserAPI(MethodView): def get(self): return "This is a GET request" def post(self): return "This is a POST request" def put(self): return "This is a PUT request" def delete(self): return "This is a DELETE request” app.add_url_rule('/', view_func=UserAPI.as_view('users'))

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RETURN A TEMPLATE. 15

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16 from flask import Flask, render_template app = Flask(__name__) @app.route("/") def index(): user = "Rag. Fantozzi" return render_template("index.html", user=user) if __name__ == "__main__": app.run()

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BLUEPRINT. 17

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18 from flask import Blueprint, render_template simple_page = Blueprint('simple_page', __name__, template_folder='templates') @simple_page.route('/') @simple_page.route('/') def show(page=None): if page is not None: return render_template('pages/%s.html' % page) else: return render_template('index.html')

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19 from flask import Flask from yourapplication.simple_page import simple_page app = Flask(__name__) app.register_blueprint(simple_page) if __name__ == "__main__": app.run()

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• Blueprint are not an applications • They are similar for some things • A blueprint is like a pluggable behavior for the main app 20

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USEFUL DECORATORS. 21

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• route: registers functions to handle routes • before_request: registers a function to run before request handlers • before_ﬁrst_request: is similar, but only once at start • after_request: registers a function to run after request handlers run • teardown_request: registers a function to run after request handlers run, even if they throw an exception • errorhandler: deﬁnes a custom error handler 22

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DJANGO VS FLASK. 23

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WHAT I LIKE OF DJANGO. 24

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• Full batteries (orm, form, session, user, ecc.) • Easy to add “app” • Great community • Stable • Popular 25

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BUT. 26

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• Sometimes it is much more than what you need • You need to follow Django pattern • Implement REST API is not so easy 27

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WHAT I LIKE OF FLASK. 28

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• Simple • Minimalist • Easy to learn and start • Well documented • Awesome as backend API 29

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BUT. 30

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• app = Flask(__name__) • context 31

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APP = FLASK(__NAME_) 32

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No magic, you need to share Flask instance between your ﬁles, but sometimes that can be a problem. 33

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#views.py from flask import Flask from models import db app = Flask(__name__) #models.py from flask.ext.sqlalchemy import SQLAlchemy from views import app db = SQLAlchemy(app) 34

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CIRCULAR IMPORT ! 35

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#factory.py from flask.ext.sqlalchemy import SQLAlchemy db = SQLAlchemy() def create_app(name): from flask import Flask app = Flask(name) db.init(app) return app #views.py from factory import create_app from models import db, OthersModels app = create_app(__name__) #models.py from factory import db 36

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IT WORKS BUT NOT SO PYTHONIC (???) 37

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CONTEXT 38

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Often in your ﬂask app you need to access the app context, as with app instance, sometimes that can be a problem. 39

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#factory.py … … … def make_celery(package_name, app=None): from celery import Celery app = app or create_app(package_name) celery = Celery(package_name, broker=app.config['CELERY_BROKER_URL']) celery.conf.update(app.config) TaskBase = celery.Task class ContextTask(TaskBase): abstract = True def __call__(self, *args, **kwargs): with app.app_context(): return TaskBase.__call__(self, *args, **kwargs) celery.Task = ContextTask return celery 40

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AGAIN IT WORKS BUT NOT SO PYTHONIC (???) 41

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WE ARE NOT ALONE. 42

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Tornado ? Falcon ? Wheezy Web ? Others ? 43

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SOME RESOURCES. 44

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Flask - http://ﬂask.pocoo.org Flask list - http://librelist.com/browser/ﬂask/ Miguel Grinberg - http://blog.miguelgrinberg.com/ Real Python - https://realpython.com/blog/ Google - http://goo.gl/Rps6vo 45

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THIS IS THE END. 46

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DID YOU LIKE THIS TALK ? 47

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GREAT BECAUSE I’M LOOKING FOR A PART TIME JOB. 48

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class part_time_job(): location = "Milan or remotely" current = "A wanna be data scientist" doing = ["Statistic at Bicocca", "read", "travel", "code"] knowledge = {} knowledge["Python"] = ["Django", "Flask", "Pandas", "…"] knowledge["JS"] = ["Nodejs", "AngularJS", “D3.js", "…"] knowledge["Database"] = ["PostgreSQL", "Redis", "…"] knowledge["Other"] = ["Machine learning", "much more !"] print("Do you want to hire me ?") print("My email {}@{}.com").format("barrachri", "gmail") 49

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BRAINSTORMING & QUESTIONS TIME 50