Because some of the limitations/restrictions with using google-app-engine (GAE) you need to understand that if you want to use it (i.e. python package) you need to include it in your application. That is where the benefits of a virtualenv come into play. virtualenv (when combined with pip) let you know exactly what packages you have because throughout the application development process if you need it you ‘pip-it’. Then pip gives you a clean manifest on what you have so you always know. But.. (you knew this was coming) GAE doesn’t like a virtual env. In fact if you try it you almost surely run into problems. For me it was a error along this line...
ImportError: No module named unittest
So what can I do? For me the reasons to use a virtualenv/pip combination is too compelling to simply not use it. I really like knowing what packages I willbe deploying up to the cloud and since I need to package them with my application why not? Furthermore if you are used to running in a virtualenv/pip environment or you have a somewhat stock python environment this is just a good way to keep things straight. Understanding the obvious limitation that you can’t run in a virtualenv we are going to take advantage of everything else this environment has to offer.
General Development Strategy
- Use Django. While I understand that GAE now support 1.1 I want that control left to me.
- Keep the development tree streamlined for the entire site. Guido recommends (as I understand him in this video ~11:45) to use a single app-engine application per independent application. This doesn’t make much sense to me as the ability to share information between different models is really extending the multi-dimensionality of the site. So my preference is to keep it all under one hood.
- Use revision control (for me it’s perforce - I don’t have anything against the others (hg/git/svn) it’s just what I like)
- Use eclipse/pydev as my development environment
I am developing for $SITE ( i.e export SITE=“foobar.com”)
/dev
/<$SITE>
/bin
/lib
/include
/src
/django
/www
app.yaml
/appengine_django
manage.py
main.py
/apps
/app_1
/app_2
/app_3
/app_n
/settings
__init__.py
urls.py
django symlink to ../src/django/django
Getting started
Setup your virtualenv
cd dev
Build up a baseline virtualenv
virtualenv --python=python2.5 --no-site-packages ${SITE}
Install some needed apps.. (make sure you are in your dev directory..)
# pip install -E ${SITE} -e svn+http://code.djangoproject.com/svn/django/trunk#egg=Django
# pip install -E ${SITE} -e svn+http://code.djangoproject.com/svn/django/tags/releases/1.1.1/#egg=Django
pip install -E ${SITE} -e svn+http://code.djangoproject.com/svn/django/tags/releases/1.1/#egg=Django
pip install -E ${SITE} yolk
*Notes: 1.1.1 failed 2 tests and trunk failed more.. 1.1 passes all tests
Activate your virtualenv
source ${SITE}/bin/activate
Create your www tree (this is where we house our app). Use the google-app-engine-django helper stuff. It’s well worth it!!
cd ${SITE}
svn export http://google-app-engine-django.googlecode.com/svn/trunk/ www
Link in your django tree
cd www
ln -s ../src/django/django
At this point you should be able to deactivate yourself and simply verify everything works.
deactivate
python2.5 manage.py test
#Ran 61 tests in 8.058s
python2.5 manage.py runserver
Now open up a web browser to http://127.0.0.1:8000/ and you should get the famous “It works!!”. At this point you should also configure the Google App Engine Launcher to point to your site directory and “www” will be your application.
Build up a quick index and push it to the web.
This is not for the faint. I am going to quickly build up a basic django index page. I want to show it works and we con complete the process.
Shuffle around my tree (personal preference)
Like I indicated above I like to have my apps all under a single apps tree (keep it clean). I also like to put settings.py under a settings tree - this allows me to mess with the __init__.py
So with that hang on..
cd ${SITE}/www
mkdir settings
mv settings.py settings/__init__.py
rm settings.pyc
mkdir apps
python2.5 manage.py startapp core
mv core apps/
Build your simple app
Edit your ${SITE}/www/urls.py
urlpatterns = patterns('',
url(r'^', include('apps.core.urls')),
)
Add in your app to the ${SITE}/settings/__init__.py
INSTALLED_APPS = (
'appengine_django',
'apps.core',
)
Create your apps/core/views.py
from django.http import HttpResponse
def index(request):
return HttpResponse('Hello World -- Django rocks!!')
Get your apps/core/urls.py ready to accept the index view
from django.conf.urls.defaults import *
import views
urlpatterns = patterns('',
url(r'^$', views.index),
)
Verify it works.. Voila - pretty simple eh??
Next up publish it..
References:
Guido's screencast - it was awesome..
Rapid Development with Python, Django, and Google App Engine (2008 Google I/O Session Videos and Slides)
