Introduction

This is a tutorial on getting the basic tutorial code for Pyramid running on appengine. Its based on predefined project. A paster based template to build the project will come later.

Details

This setup assumes your using linux. Code and buildout config for the tutorial is found at http://bfg-pages.googlecode.com/svn/pyramid-gae-tutorial/trunk

Setup

To do the setup I am going to use a buildout recipe developed by Rodrigo Moraes <rodrigo moraes at gmail com>. Recipe at http://pypi.python.org/pypi/appfy.recipe.gae/0.9.1.

Make a directory for your tutorial.

timh@chrome:~$ mkdir tut1
timh@chrome:~$ cd tut1

Then setup virtualenv so you can install the buildout recipe.

timh@chrome:~/tut1$ virtualenv --no-site-packages --python=/usr/bin/python2.5 .
Running virtualenv with interpreter /usr/bin/python2.5
New python executable in ./bin/python2.5
Also creating executable in ./bin/python
Installing setuptools............done.

Don't activate the virtualenv. Use explicit paths when referencing scripts set up by virtualenv.

Now use easy_install to install the appfy.recipe.gae

timh@chrome:~/tut1$ ./bin/easy_install appfy.recipe.gae

Next check out the sample app which has the bootstrap and buildout configs to be used for the rest of the tutorial.

timh@chrome:~/tut1$
timh@chrome:~/tut1$ svn checkout http://bfg-pages.googlecode.com/svn/pyramid-gae-tutorial/trunk app
A    app/default_error.html
A    app/settings.yaml
A    app/app.yaml
A    app/pkg_resources.py
A    app/views.py
A    app/bootstrap.py
A    app/buildout.cfg
A    app/lib
A    app/lib/dist
A    app/utils.py
A    app/static
A    app/static/logo.png
A    app/static/pylons.css
A    app/static/favicon.ico
A    app/tests.py
A    app/models.py
A    app/main.py
A    app/templates
A    app/templates/mytemplate.pt
Checked out revision 159.

Next we need to create some symlinks to varios .cfg files required for buildout.

timh@chrome:~/tut1$ ln -s app/buildout.cfg 
timh@chrome:~/tut1$ ln -s app/bootstrap.py 
timh@chrome:~/tut1$ ln -s app/gaetools.cfg 
timh@chrome:~/tut1$ ln -s app/versions.cfg 

make a var/downloads so that buildout can cache its downloads.

timh@chrome:~/tut1$ mkdir -p var/downloads

Then run bootstrap.py which sets up the environment (this will use distribute)

timh@chrome:~/tut1$ ./bin/python bootstrap.py 

... stuff happens ...

Now run buildout, which will download and install pyramid and all of it's dependancies in app/lib/dist. This recipe unpicks the eggs and only deploys the required files.

timh@chrome:~/tut1$ ./bin/buildout

... stuff happens ...

timh@chrome:~/tut1$

Now start the dev server.

timh@chrome:~/tut1$ bin/dev_appserver app
INFO     2010-12-03 15:24:27,784 appengine_rpc.py:153] Server: appengine.google.com
WARNING  2010-12-03 15:24:27,788 datastore_file_stub.py:573] Could not read datastore data from /home/timh/tut1/var/data.store
INFO     2010-12-03 15:24:27,816 dev_appserver_main.py:485] Running application pyramid-gae-tutorial on port 8080: http://localhost:8080
WARNING  2010-12-03 15:24:33,924 main.py:20] Starting main

Point your web browser at http://localhost:8080/ and something similar to below will appear in the terminal

INFO     2010-12-03 15:24:34,171 dev_appserver.py:3317] "GET / HTTP/1.1" 200 -

This sample app has been deployed on appspot. You can see it at http://pyramid-gae-tutorial.appspot.com/

Details of the sample app

Now lets look at the difference between this sample app and the one in the original tutorial.

things to discuss.

whats in the app

   + app
      + lib
         + dist
            #unpicked pyramid and it's dependancies
            + chameleon  
            + mako  
            + markupsafe  
            + paste  
            + pyramid  
            + README.txt  
            + repoze  
            + simplejson  
            + tests  
            + translationstring  
            + venusian  
            + webob  
            + zope
 
      app.yaml
      default_error.html
      main.py
      pkg_resources.py
      + static
         favicon.ico  
         logo.png  
         pylons.css

      + templates
          mytemplate.pt

      tests.py
      views.py

You will also note there are the .cfg files that you created the symlink to eariler. These are not part of the appengine application. (I need to stick them somewhere else ;-)

The contents of lib are as a result of running buildout, which installs pyramid from PyPI eggs and all of its dependancies and then proceeds to copy the actual code from the eggs to lib/dist (I need to move everything up to dist, thats a hold over from the original recipe for tipfy, which I am leveraging off)

main.py

import logging

logging.getLogger().setLevel(logging.INFO)

import sys,os

sys.path.insert(0,'lib/dist')

from pyramid.configuration import Configurator
from models import get_root
from google.appengine.ext.webapp.util import run_wsgi_app

settings = {
    'reload_templates': 'false',
    'debug_authorization': 'false',
    'debug_notfound': 'false',
    'debug_templates': 'false',
    'default_locale_name': 'en',
}

def main():
    """ This function runs a Pyramid WSGI application.
    """
    
    config = Configurator(root_factory=get_root,settings=settings)
    config.add_view('views.my_view',
                    context='models.MyModel',
                    renderer='templates/mytemplate.pt')
    app = config.make_wsgi_app()
    run_wsgi_app(app)
            
if __name__ == '__main__':
  main()

• run_wsgi_app
• settings
• debugging with pdb
• static handlers.
• default_error handler
• app.yaml
• configuring chameleon

Deploying the app

• appcfg

Running tests

put stuff here ...

Some important info/links for appengine

Import things to note

here are some random things a pyramid developer new to appengine needs to know.

• appengine runs python 2.5 in production. Do not be even tempted to run python 2.6 or later. You have been warned ;-)
• appengine runs multiple single threaded instances of your code, to service the requests.
• instances of your app can only share state/information via the datastore or memcache.
• web requests must run within 30seconds.
• startup time for a cold instance is crucial.
• Try and defer things if you can. For instance don't load up a deform/formish schemas for forms until you actually need them.
• do all you configuration imperatively. zcml and scan is slower.
• You can not write to the filesystem in appengine.

Important links to documents and/or resources

• Read Nick Johnsons blog. http://blog.notdot.net/
• Appengine docs. http://code.google.com/appengine/docs/python/gettingstarted/