Migrating to Python 2.7, part 2: Webapp and templates

In part 1 of the migration series, we discussed changes to your app to take advantage of the 2.7 runtime's support for multithreading. Today, we'll start looking at the changes to the included libraries, and how we'll have to modify our app to use them.


First up is the replacement of App Engine's lightweight webapp framework with webapp2. Webapp2 is an external open-source project, which says it "follows the simplicity of webapp, but improves it in some ways: it adds better URI routing and exception handling, a full featured response object and a more flexible dispatching mechanism". Webapp2 does an excellent job of maintaining compatibility with webapp, which is why it was chosen as a replacement, but it also adds a number of useful improvements on it.

To see what's changed in concrete terms, let's assume we have a very straightforward app that looks something like this:

import os

from google.appengine.ext import webapp
from google.appengine.ext.webapp import template

class BaseHandler(webapp.RequestHandler):
  def render_template(self, filename, **template_args):
	path = os.path.join(os.path.dirname(__file__), 'templates', filename)
	self.response.out.write(template.render(path, template_args))

class IndexHandler(BaseHandler ...

Using BlobReader, wildcard subdomains and webapp2

Today we'll demonstrate a number of new features and libraries in App Engine, using a simple demo app. First and foremost, we'll be demonstrating BlobReader, which lets you read Blobstore blobs just as you would a local file, but we'll also be trying out two other shinies: Wildcard subdomains, which allow users to access your app as anything.yourapp.appspot.com (and now, anything.yourapp.com), and Moraes' excellent new webapp2 library, a drop-in replacement for the webapp framework.

Moraes has built webapp2 to be as compatible with the existing webapp framework as possible, while improving a number of things. Improvements include an enhanced response object (based on the one in webob), better routing support, support for 'status code exceptions', and URL generation support. While the app we're writing doesn't require any of these, per-se, it's a good opportunity to give webapp2 a test drive and see how it performs.

But what are we writing, you ask? Well, to show off just how useful BlobReader is, I wanted something that demonstrates how you can use it practically anywhere you can use a 'real' file object - such as using it to read zip files from ...