Building a Google AppEngine webapp with Python


Today I wanted to add ReCAPTCHA to one of my web applications built with NodeJS. A quick look on my heroku dashboard showed that the application wasn’t even running anymore, and a quick search through the logs showed that I was running into a quota of the connected Redis to go instance. Before doing any real work I’d have to upgrade the underlying stack, and searching for recaptcha clients for NodeJS did not bring up anything useful for me.

So, I decided to completely switch technology and rebuild the application using Google AppEngine and Python. :)

I closely followed the python tutorial for the first steps, creating a simple application that could store and display a single Entity of type Highlight. I then proceeded to add jinja2 templates. All of this is pretty straight forward and the application was up and running after two hours.

But then I stumbled upon a strange error: When I tried to read Entities by key from the Datastore, I couldn’t get the stored Entities back. After researching, I finally found the correct documentation and this code finally let me retrieve stored Highlight entities from the Datastore:

# get key via URL parameter 'safeKey'
# generated via myEntity.key.urlsafe()
k = ndb.Key(urlsafe = safeKey)
highlight = k.get()

Previously I used something like this:

safeKey = myEntity.key.id()
...
Highlight.get_by_id(safeKey)

This did not return any result, although I could verify via the appengine dashboard that there really was an Entity in the Datastore with the given ID.

Anyways, you can now store syntax highlighted code at http://perfect-embassy-830.appspot.com/

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