wware / django-examples

Simple examples of little Django websites

Django examples

Since my profession now seems to be "Django guy", I might as well maintain a little collection of Django examples, branching off from the standard tutorial.

Heroku

I'm going to run this stuff on Heroku just for convenience. It works and it's free. I'd need to do some research if I were trying to deploy something seriously.

Django uses PostgreSQL. When I'm just messing around on the Macbook, I use SQLite.

The deployment command git push heroku master did not create or sync my PostgreSQL database. But I found there is a Python shell command that can do the job:

$ heroku run python manage.py syncdb

Some info about Python, Django, Gunicorn, and Heroku all playing together...

• https://devcenter.heroku.com/articles/getting-started-with-python
• https://devcenter.heroku.com/articles/getting-started-with-django
• https://docs.djangoproject.com/en/dev/howto/deployment/wsgi/gunicorn/#running-django-in-gunicorn-as-a-generic-wsgi-application
• http://docs.gunicorn.org/en/latest/run.html
• http://michal.karzynski.pl/blog/2013/06/09/django-nginx-gunicorn-virtualenv-supervisor/

Trouble with the tutorial

One thing in the standard tutorial that didn't work for me is the section on Removing hardcoded URLs in templates in the third part of the tutorial. I got the following error when I tried it, and have done only a little digging to try to understand what's happening:

Reverse for ''detail'' with arguments '(1,)' and keyword arguments '{}' not found.

So I did a little digging, and in venv/lib/python2.7/site-packages/django/template/defaulttags.py I found URLNode.render which has this:

try:
    url = reverse(project_name + '.' + view_name,
              args=args, kwargs=kwargs,
              current_app=context.current_app)
except NoReverseMatch:
    if self.asvar is None:
        # Re-raise the original exception, not the one with
        # the path relative to the project. This makes a
        # better error message.
        raise e

And project_name says "mysite" instead of "polls". If I try to force the matter by saying this in mysite.settings:

SETTINGS_MODULE = polls.settings

things don't go too much better. Yes, I get project_name saying "polls", but then polls hasn't been imported when we need it for the reverse call. Since this removal of hardcoded URLs appears to be a matter of taste, useful for very large websites but unnecessary for small ones, I will defer further investigation to another time.

Other stuff I'd like to do

Priority queue

A to-do list should really be a priority queue. If it's maintained online, accessible to phone or tablet or Macbook, that's a handy thing. Python has a heap queue module designed for priority queues. I don't think that will be necessary for this purpose since my to-do list might never have more than 100 items, and I might redefine priorities from time to time. I might have a few different characteristics, which make it possible to sort in a number of different ways.

In any event one of the apps should be a priority queue, however it is implemented.

Responsive web design

I want to learn this stuff so I can make websites that work well on phones, tablets, and laptops.

APIs of the Rich and Famous

• https://developers.google.com/drive/examples/python DrEdit, an example usage of the Google Drive API
• https://developers.google.com/events/io/sessions/351310959 The Freebase APIs: Tapping into Google's Knowledge Graph
• https://developers.google.com/maps/ Google Maps API

Database cleverness

There is a bunch of Django stuff for optimizing SQL queries involving select_related, prefetch_related, only, and exclude, and those would be good to learn more about. So database stuff, joins, prefetching, etc., all the QuerySet API stuff in Django.

PayPal and e-commerce

PayPal maintains a sandbox for debugging your application, and I should use the REST APIs to work with the sandbox.

There are some pre-existing e-commerce solutions for Django, such as Satchmo and LFS which are both open-source. There is also Beginning Django E-Commerce, a book on Amazon with 4.5 stars and an affordable Kindle edition.

I should build a simple fake webstore with a shopping cart and a PayPal payment system, using the sandbox. It should be trivially easy to flip a switch to make it a real webstore. Obviously flipping the switch would include replacing fake products with real products.

Try to think through how you'll handle orders and fulfillment. There is a customer-facing piece and a merchant-facing piece, and the merchant-facing piece should help the merchant in getting stuff to customers in a timely fashion, and keeping track of any inventory.

Minor diversion: automation of science

Here are some papers by Ross D. King, the Adam robot scientist guy.

• http://ceur-ws.org/Vol-611/paper10.pdf
• http://www.biomedcentral.com/content/pdf/1471-2105-9-97.pdf
• http://www.bioontology.org/sites/default/files/on%20the%20fomalization%20and%20reuse.pdf
• http://commonsenseatheism.com/wp-content/uploads/2011/02/King-The-Automation-of-Science.pdf

The guy is very much aligned with my own thinking about this stuff, but of course his thoughts are vastly more detailed because he's actually built the machine, made it do science, and published papers as a result. Regrettably, he appears to be working in nearly complete obscurity.

My hope is that PyLD will make it possible and/or easy to build semantic web services that help with the automation of science.