Chris Marasti-Georg Chris Marasti-Georg - 4 months ago 9
Python Question

Project structure for Google App Engine

I started an application in Google App Engine right when it came out, to play with the technology and work on a pet project that I had been thinking about for a long time but never gotten around to starting. The result is BowlSK. However, as it has grown, and features have been added, it has gotten really difficult to keep things organized - mainly due to the fact that this is my first python project, and I didn't know anything about it until I started working.

What I have:


  • Main Level contains:

    • all .py files (didn't know how to make packages work)

    • all .html templates for main level pages


  • Subdirectories:

    • separate folders for css, images, js, etc.

    • folders that hold .html templates for subdirecty-type urls




Example:

http://www.bowlsk.com/ maps to HomePage (default package), template at "index.html"

http://www.bowlsk.com/games/view-series.html?series=7130 maps to ViewSeriesPage (again, default package), template at "games/view-series.html"

It's nasty. How do I restructure? I had 2 ideas:


  • Main Folder containing: appdef, indexes, main.py?


    • Subfolder for code. Does this have to be my first package?

    • Subfolder for templates. Folder heirarchy would match package heirarchy

    • Individual subfolders for css, images, js, etc.


  • Main Folder containing appdef, indexes, main.py?


    • Subfolder for code + templates. This way I have the handler class right next to the template, because in this stage, I'm adding lots of features, so modifications to one mean modifications to the other. Again, do I have to have this folder name be the first package name for my classes? I'd like the folder to be "src", but I don't want my classes to be "src.WhateverPage"




Is there a best practice? With Django 1.0 on the horizon, is there something I can do now to improve my ability to integrate with it when it becomes the official GAE templating engine? I would simply start trying these things, and seeing which seems better, but pyDev's refactoring support doesn't seem to handle package moves very well, so it will likely be a non-trivial task to get all of this working again.

Thanks.

Answer

First, I would suggest you have a look at "Rapid Development with Python, Django, and Google App Engine"

GvR describes a general/standard project layout on page 10 of his slide presentation.

Here I'll post a slightly modified version of the layout/structure from that page. I pretty much follow this pattern myself. You also mentioned you had trouble with packages. Just make sure each of your sub folders has an __init__.py file. It's ok if its empty.

Boilerplate files

  • These hardly vary between projects
  • app.yaml: direct all non-static requests to main.py
  • main.py: initialize app and send it all requests

Project lay-out

  • static/*: static files; served directly by App Engine
  • myapp/*.py: app-specific python code
    • views.py, models.py, tests.py, __init__.py, and more
  • templates/*.html: templates (or myapp/templates/*.html)

Here are some code examples that may help as well:

main.py

import wsgiref.handlers

from google.appengine.ext import webapp
from myapp.views import *

application = webapp.WSGIApplication([
  ('/', IndexHandler),
  ('/foo', FooHandler)
], debug=True)

def main():
  wsgiref.handlers.CGIHandler().run(application)

myapp/views.py

import os
import datetime
import logging
import time

from google.appengine.api import urlfetch
from google.appengine.ext.webapp import template
from google.appengine.api import users
from google.appengine.ext import webapp
from models import *

class IndexHandler(webapp.RequestHandler):
  def get(self):
    date = "foo"
    # Do some processing		
    template_values = {'data': data }
    path = os.path.join(os.path.dirname(__file__) + '/../templates/', 'main.html')
    self.response.out.write(template.render(path, template_values))

class FooHandler(webapp.RequestHandler):
  def get(self):
    #logging.debug("start of handler")

myapp/models.py

from google.appengine.ext import db

class SampleModel(db.Model):

I think this layout works great for new and relatively small to medium projects. For larger projects I would suggest breaking up the views and models to have their own sub-folders with something like:

Project lay-out

  • static/: static files; served directly by App Engine
    • js/*.js
    • images/*.gif|png|jpg
    • css/*.css
  • myapp/: app structure
    • models/*.py
    • views/*.py
    • tests/*.py
    • templates/*.html: templates
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