Twisted Klein: Basics

Basics: Routes, Methods, Variables

This section contains many similarities with Flask.  So if you know how to perform basic Flask-style routing, this section can be skipped.  Just keep in mind that a request parameter must be passed in all route functions.  Example::

      app.route('/')
   def example(request):
       #...

Web frameworks have come a long way, especially in Python.  A major contributing factor is the dead simple routing syntax from Flask, Bottle, Hug, etc.  Klein shares syntactical similarities with those frameworks for the most part.  The only key difference is the request parameter that gets passed into the functions after specifying the route.  However we won't worry about that for now.  Let’s dive into Klein with a simple Hello World application.

Routes *aka* Hello World

helloworld.py

from klein import Klein

app = Klein()

@app.route('/')
def root(request):
    return 'Welcome'

@app.route('/hello')
def hello(request):
    return 'Hello World' 

app.run(host='localhost', port=9000)

To start the Klein application, simply execute the Python script:

python helloworld.py

The app.run() function will create a web server listening on the localhost interface on port 9000.  Change the host and ports according to your requirements.  app.route() creates the endpoints for your application, so in our snippet, there's the default route and a route for /hello.  A quick test can be done in a web browser by navigating to http://localhost:9000 or by using the curl utility:

curl localhost:9000
curl localhost:9000/hello

Return Types

Klein accepts bytes, ASCII encoded string, Twisted Resource, Twisted Renderable, or Deferred objects as return types.  Ensure the route functions only return one of these types.

HTTP Methods

The HTTP methods GET, POST, PUT, DELETE are common amongst web applications.  In Klein, routes can be explicitly tied to HTTP methods by passing in a list of the methods names via a parameter aptly called methods.  If no explicit method is specified, then all methods will be accepted.

import json
from klein import Klein

app = Klein()
@app.route('/')
def root(request):
    return 'Welcome'

@app.route('/methods', methods=['POST', 'delete'])
def specificMethods(request):
    return json.dumps({
        'boolean': True,
        'int': 1,
        'list': [1,2,3]
    })

The /methods endpoint will output JSON data if and only if the endpoint is accessed using the POST or DELETE methods (note that methods are not case sensitive).  Where as the "/" route can be accessed by any method since no explicit methods are specified.

curl -X POST localhost:9000/methods
curl -X DELETE localhost:9000/methods
curl -X POST localhost:9000

# this will fail
curl -X GET localhost:9000/methods

Speaking of “any method”, custom methods can also be used.  For instance, let’s say your application requires a method called “GOOGLE”.  All that needs to be done is to add “GOOGLE” to the list of methods then check using curl -X GOOGLE.

@app.route('/methods', methods=['POST', 'delete', 'GOOGLE'])

Variables

Variables works by simply appending a variable name surrounded by angle brackets to the URL string.  Variables allow for your app to take in any string parameter and use it in the function corresponding to the route.  As an example, the following will display a message followed by a name passed in from the URL:

@app.route('/hello/<name>')
def helloName(request, name):
    return 'Hello %s!' % name

Optionally, a type specifier can be supplied so that the string variable will be cast to a specified type.  This allows variables to be validated without extraneous code.  Out of the box, the specifiers are int, float, and path.

@app.route('/hello/<name>/<int:age>')
def helloNameAge(request, name, age):
    if age <= 1:
        return '%s is just starting life.' % name
    elif age >= 2 and age <= 29:
        return 'Name: %s. Age: %d. So young!' % (name, age)
    return 'Name: %s. Age: %d! So old!' % (name, age)

Final Example

import json
from klein import Klein

app = Klein()

@app.route('/')
def root(request):
    return 'Welcome'

@app.route('/hello')
def hello(request):
    return 'Hello World'

@app.route('/hello/<name>')
def helloName(request, name):
    return 'Hello %s!' % name

@app.route('/hello/<name>/<int:age>')
def helloNameAge(request, name, age):
    if age <= 1:
        return '%s is just starting life.' % name
    elif age >= 2 and age <= 29:
        return '%s is %d years old. You are so young!' % (name, age)
    return '%s is %d years old! You are so old!' % (name, age)

@app.route('/methods', methods=['POST', 'delete', 'Google'])
def specificMethods(request):
    return json.dumps({
                      'boolean': True,
                      'int': 1,
                      'list': [1,2,3]
                    })