App Engine Support

Pecan runs smoothly in Google's App Engine. There is no hacking/patching or weird changes that you need to make to work with Pecan. However, since App Engine has certain restrictions you may want to be aware of how to set it up correctly.

Note

We do not discuss here how to get an App Engine environment here, nor App Engine specifics that are not related to Pecan. For more info on App Engine go to their docs

Dependencies

Pecan has a few dependencies and one of them is already supported by App Engine (WebOb) so no need to grab that. Just so you are aware, this is the list of things that you absolutely need to grab:

simplegeneric >= 0.7

Paste >= 1.7.5.1

These are optional, depending on the templating engine you want to use. However, depending on your choice, you might want to check the engine's dependencies as well. The only engine from this list that doesn't require a dependency is Kajiki.

Genshi >= 0.6

Kajiki >= 0.2.2

Mako >= 0.3

From this point forward, we will assume you are getting Kajiki, to avoid describing third party dependencies.

Creating the project

Create a directory called pecan_gae and cd into it so we can start adding files. We go step by step into what needs to go there to get everything running properly.

app.yaml

To start off, you will need your app.yaml file set properly to map to Pecan. This is how that file should look like:

application: foo-bar
version: 1
runtime: python
api_version: 1

handlers:

- url: /.*
  script: main.py

Remember the application name will have to match your registered app name in App Engine. The file above maps everything to a main.py file.

This file will be the root of our project and will handle everything.

main.py

You can name this anything you want, but for consistency we are going with main.py. This file will handle all the incoming requests including static files for our Pecan application. This is how it should look:

from google.appengine.ext.webapp import util
import sys
if './lib' not in sys.path:
    sys.path.append('./lib')

from pecan import Pecan, expose


class RootController(object):

    @expose('kajiki:index.html')
    def index(self):
        return dict(name="Joe Wu Zap")


def main():
    application = Pecan(RootController(), template_path='templates')
    util.run_wsgi_app(application)


if __name__ == '__main__':
    main()

We are doing a few things here... first we are importing the util module from App Engine that will run our Pecan app, then we are importing sys because we need to add lib to our path.

The lib directory is where all our dependencies (including Pecan) will live, so we need to make sure App Engine will see that as well as all our libraries within lib (it would not be enough to add a __init__.py file there.

templates

The templates directory is where we will have all of our html templates for Pecan. If you don't have it already, go ahead and create it and add this html file to it and name it index.html:

<html>

<head>
  <title>Hello, ${name}!</title>  
</head>

<body>
  <h1>Hello, ${name}!</h1>
</body>

</html>

lib

The lib directory should contain the source for all the dependencies we need. For our example, it should contain 3 libraries:

kajiki

paste

pecan

That is all you need to get this project started!

Note

When grabing the source of the dependencies we mention, make sure you are actually grabing the module itself and not adding the top directory source (where setup.py lives)

Layout

This is how your layout (only showing directories) should look like:

pecan_gae
|____app.yaml
|____lib
| |____kajiki
| | |____tests
| |   |____data
| |____paste
| | |____auth
| | |____cowbell
| | |____debug
| | |____evalexception
| | | |____media
| | |____exceptions
| | |____util
| |____pecan
|____templates

Trying it out

Now everything should be ready to start serving, so go ahead and run the development server:

$ ./dev_appserver.py pecan_gae 
INFO     2010-10-10 12:44:29,476 dev_appserver_main.py:431] Running application pecan-gae on port 8080: http://localhost:8080

If you go to your browser and hit localhost:8080 you should see something like this:

Hello, Joe Wu Zap!

This is the most basic example for App Engine, you can start adding more controllers to handle a bigger application and connect everything together.

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