Twisted Klein: Expanding Your App

Expanding Your App

Subroutes

Let’s start with a simple way to combine routes that share a common endpoint. For example, lets say we need routes for /base/first, /base/second, /base/third. The crude way of achieving this would be to explicitly write out each route with the /base route, like so:

app.route('/base/first')
def first(request):
    # ...

app.route('/base/second')
def second(request):
    # ...

app.route('/base/third')
def third(request):
    # ...

This is valid code, but there’s simpler syntax that can help reduce some common human errors like misspellings. The subroute function helps make the code more legible as well as simpler.

with app.subroute('/base') as sub:

    @sub.route('/first')
    def first(request):
        return 'first'

    @sub.route('/second')
    def second(request):
        return 'second'

    @sub.route('/third')
    def third(request):
        return 'third'

Expanding

It’s an inevitable fact that your application will grow and it may prove useful to import Klein objects from another module. Without going into great detail, Klein can handle nested routes by passing in branch=True in the route decorator, which allows then additional endpoints can be exposed. The route function should return Twisted a Resource object, which contain endpoints of their own. The actual implementation is much easier and less intimidating so please read on!

Static Files

Static files are a perfect way to illustrate how branching works. The following example will serve the files at a specific local directory.

from twisted.web.static import File

@app.route('/static', branch=True)
def static(request):
    return File('/path/to/static/files')

Notice the branch keyword in the route decorator. The branch syntax simply means there are other Resources (aptly labeled leaves) under this route. File objects return a Resource object for every file in the path.

Distributed Modules

Imagine the application you’ve built has grown large enough that placing all the routes in a single file has become too unwieldy. Expanding on the branch concept, we can generate the Resource file from other Klein objects, making it possible to simply import Klein objects.

blueprints.py

app = Klein()

@app.route('/hello')
def index(request):
    return 'Hello from the subroutes example'

with app.subroute('/blue') as sub:
    @sub.route('/first')
    def first(request):
        return 'first'

    @sub.route('/second')
    def second(request):
        return 'second'

    @sub.route('/third')
    def third(request):
        return 'third'

Now lets use this in another klein application.

from klein import Klein
from twisted.web.static import File

import blueprints    # this module holds the other Klein app

app = Klein()

@app.route('/branch', branch=True)
def branchOff(request):
    return blueprints.app.resource()        # get the Resource object

@app.route('/branch/2/', branch=True)
def branchAgain(request):
    return blueprints.app.resource()     # get the Resource object

For those who are familiar, this is similar to Flask and their concept of Blueprints. In my personal opinion, I favor Klein’s approach as it contains less obscure function calls.

Final Examples

• static.py
• blueprints.py
• branching.py

References

• How to Use Resources
• Resource API