Some basic couchdbkit 'views' (get it?)

We had to go to LA this weekend and I made my wife drive so I could learn up on CouchDB views. I had to re-read the Design Document and View sections of my O'Reilly book a couple times before it really clicked. Thankfully, the book is detailed enough that I didn't need to be looking at a database through Futon to get the point.

So today I hacked together a simple view in a Python script. This returns all my documents with a .symbol of 'C'. I'm not good at JavaScript (yet) so this is about as advanced as I want to get as I focus on Python and CouchDB:

design_doc = {
    '_id': '_design/test',
    'language': 'javascript',
    'views': {
        'allcitis': {
            "map": """function(doc) { if (doc.symbol == "C") { emit(doc._id, doc); }}"""
            }
        }
    }
frenzydb.save_doc(design_doc)

No problem - worked the first time and I saw it my Cloudant database. Parsing the view results through couchdbkit to a little longer to figure out. The Getting Started page ends with:

greets = Greeting.view('greeting/all’)

It took me a little while to figure out 'greets' wasn't a list, it's a couchdbkit.client.ViewResults. As it says in the comments for couchdbkit/client.py, "It return an ViewResults object on which you could iterate, list, ...". Okay great, throw it in a list. Here's a trivial function to get the average of 'price' using the aforementioned view:

citis = list(frenzydb.view('/test/allcitis'))

sum = 0
for citi in citis:
    sum += float(dict(citi['value'])['price'])
print round(sum / len(citis), 2)

Google App Engine is pretty great (if you go all the way)

So I'm starting to bang around another project. As I describe it on my Careers 2.0 profile:

Project is still in its infancy but it will have server (GAE-hosted Python program evaluating JSON feeds of stock data with Cloundant [CouchDB] backend) and mobile (Android app to visualize/manipulate the data from Cloundant) components. There really isn't a point behind this program and I don't necessarily condone algorithmic trading - it's just a fun hack.

Or so I thought. Doesn't look like I'll be using Google App Engine because I don't want to do it the "GAE way" (not that there's anything wrong with that). Deploying an app to GAE is super simple but I ran into problems when starting to incorporate 3rd-party libraries (couchdbkit and restkit to be exact). These libs are too small to be part of the standard runtime environment. It's interesting to note that even Django is implemented in a slightly different way on GAE.

I'll spare the details (though they are available in my stackoverflow question) but I was having importing couchdbkit into my script. It was choking on things likes sockets and resources, which made me think I was running afoul of the sandbox rules:

An App Engine application cannot:

• write to the filesystem. Applications must use the App Engine datastore for storing persistent data. Reading from the filesystem is allowed, and all application files uploaded with the application are available.
• open a socket or access another host directly. An application can use the App Engine URL fetch service to make HTTP and HTTPS requests to other hosts on ports 80 and 443, respectively.
• spawn a sub-process or thread. A web request to an application must be handled in a single process within a few seconds. Processes that take a very long time to respond are terminated to avoid overloading the web server.
• make other kinds of system calls.

I put a question on the Cloudant discussion board and got not 1 but 2 answers from Cloudant techs within an hour (these dudes are good - I don't even have a paying account and they are very responsive). Anyway, they tipped me off to this telling Quora answer. It looks like the Django/Python hosting space is about to blow up with Heroku-like solutions.

Both the Cloudant tech and Django responder (a Django co-inventor) had good things to say about WebFaction. It is not a free hosting service ($9.50 per month and goes down with longer term contracts). After a quick Q&A session with a sales rep, I took the plunge. 1 hour later, my program was working perfectly on my WebFaction account. Success! The only thing that makes me nervous is having to do any sys admin stuff at all - getting my script and installations to reference the right Python version (WebFaction comes everything from 2.4 [default] up through 3.2) is about all I care to handle.

Python + Couchdbkit = nice

So I'm working on a CouchDB project and you can read more about what I'm doing on the mobile side here.. There will be a server-side component and I want to get my feet wet with Python. I'm currently working through the tutorial but like most people I learn more by doing.

There are several CouchDB libraries for Python but I went with Couchdbkit. This decision was influenced by a post on the Cloudant discussion board stating Couchdbkit and Cloudant should work well together. So far, I have to agree.

The installation instructions for Couchdbkit are pretty straight forward. For the record, I'm using Python 2.6.6. I did find I needed to use restkit for HTTP resources. I set my sights low - I just wanted to get the program of Couchdbkit's Getting Started page to work. Username/password redacted to protect the innocent:

#! /usr/bin/env python

import datetime
from couchdbkit import *
from restkit import BasicAuth

class Greeting(Document):
    author = StringProperty()
    content = StringProperty()
    date = DateTimeProperty()

server = Server('https://[username].cloudant.com/', filters=[BasicAuth('[usename]', '[password]')])
db = server.get_or_create_db("greeting")

Greeting.set_db(db)
greet = Greeting(
    author="Benoit",
    content="Welcome to couchdbkit world",
    date=datetime.datetime.utcnow()
)
greet.save()


There are more exercises on the Getting Started page including an introduction to views. This worked as advertised with no need to change the supplied code.