This document introduces Flask, a Python microframework for building web applications and APIs. It shows how to create a basic "Hello World" Flask app in 3 steps: creating the Flask object, defining a route, and returning a JSON response. It then demonstrates various response types like simple text, generators, and files. It covers routing concepts like dynamic routes, default values, and REST verbs. More advanced topics discussed include static file serving, database connections, exception handling, and using blueprints to organize routes.

1. Flask RESTful Services
There is an alternative to DJango
http://flask.pocoo.org/

2. Who Am I?

3. Why Flask?
Simple
Intuitive
Loads of Extensions
Pythonic

4. Hello World in 3 Steps
from flask import Flask, jsonify
app = Flask(__name__)
@app.route("/")
def root():
msg = {"message": "Hello World"}
return jsonify(msg)
if __name__ == "__main__":
app.run()
1. Creation of the Flask App
2. Define Route
3. Return dictionary as JSON

5. 1. Response

6. Simple Response
@app.route("/simple/")
def return_simple():
return "I lost it", 404

7. Returning a Generator
@app.route("/generator/")
def return_generator():
def loads_of_data():
yield "["
for i in xrange(5):
if i:
yield ","
yield '{ "key%d": "Entry Number %d"}' % (i, i)
yield "]"
return Response(loads_of_data(), content_type="application/json")
Generator Function

8. Returning a Response
@app.route("/response/")
def return_response():
msg = {"message": "I am working on that..."}
msg_json = json.dumps(msg)
return Response(msg_json, content_type="application/json",
status=202)
class flask.Response(response=None, status=None, headers=None,
mimetype=None,content_type=None, direct_passthrough=False)

9. Returning a File
@app.route("/file/")
def return_file():
return send_file('flask_logo.png')
flask.send_file(filename_or_fp, mimetype=None,
as_attachment=False,attachment_filename=None, add_etags=True,
cache_timeout=None,conditional=False)

10. 2. Routing

11. Dynamic Route
@app.route("/car/<make>/<model>")
def car(make, model):
car = {
"make": make,
"model": model
}
return jsonify(car)

12. Dynamic Route - Set Type
@app.route("/car/<string:make>/<int:model>")
def car(make, model):
car = {
"make": make,
"model": model
}
return jsonify(car)
Specify type of params

13. Dynamic Route - Set Default
@app.route("/car/<string:make>/<int:model>")
@app.route("/car/<string:make>/", defaults={"model": 500})
@app.route("/car/", defaults={"make": "Fiat", "model": 500})
def car(make, model):
car = {
"make": make,
"model": model
}
return jsonify(car)

14. REST Verbs
@app.route("/inventory/", methods=['POST'])
def inventory_post():
data = request.json
resp = jsonify({"idinput": data.get("id")})
resp.status_code = 201
return resp
methods allow a list of verbs
jsonify returns a Response object

15. Talk is Cheap...

16. 3. Advance-ish

17. Static File Server
@app.route('/<path:path>')
def send_app(path):
return send_from_directory('www/', path)
@app.route('/')
def send_app_index():
return send_from_directory('www/', 'index.html')

18. Database Connection
from flask import g
def get_db():
db = getattr(g, '_database', None)
if db is None:
db = g._database = connect_to_database()
return db
@app.teardown_appcontext
def close_connection(exception):
db = getattr(g, '_database', None)
if db is not None:
db.close()
http://flask.pocoo.org/docs/0.10/patterns/sqlite3/
Use Flask’s Global Object
Open connection if not connected
Close connection when request is done

19. Exception Handling
def restful_error_handler(ex):
resp = jsonify(error_message=str(ex))
if isinstance(ex, HTTPException):
resp.status_code = ex.code
else:
resp.status_code = 500
return resp
for code in default_exceptions.iterkeys():
app.error_handler_spec[None][code] = restful_error_handler
http://flask.pocoo.org/snippets/83/
Set Response Code
[<blueprint name>][<http code>]

20. Blueprint
bp = Blueprint('car', __name__)
@bp.route("/<make>/<model>"):
def return_car(make, model):
return jsonify({ "make": make, "model": model})
app.register_blueprint(bp, url_prefix='/car')
Create a Blueprint object
Declare route of the blueprint
Register blueprint

21. Putting it all together

22. More Info
http://flask.pocoo.org/
http://flask.pocoo.org/extensions/
http://docs.python-requests.org/en/latest/
https://github.com/marcoslin/flask-restful-into

23. @marcoseu
marcos.lin@farport.co.uk