First Look at Django

Django is MVC... kinda

Django (and all of the frameworks I'm looking at) is based on the "MVC" software architecture pattern. Since these are largely personal notes (can't imagine anyone else reading this) I'm not going to cover the basics here. You can find that in the Django Book or on Wikipedia.

But here's an interesting quote from Chapter 5 of the Django Book:

Because the “C” is handled by the framework itself and most of the excitement in Django happens in models, templates, and views, Django has been referred to as an MTV framework. In the MTV development pattern,

• M stands for “Model,” the data access layer. This layer contains anything and everything about the data: how to access it, how to validate it, which behaviors it has, and the relationships between the data.
• T stands for “Template,” the presentation layer. This layer contains presentation-related decisions: how something should be displayed on a Web page or other type of document.
• V stands for “View,” the business logic layer. This layer contains the logic that access the model and defers to the appropriate template(s). You can think of it as the bridge between models and templates.
  

If you’re familiar with other MVC Web-development frameworks, such as Ruby on Rails, you may consider Django views to be the “controllers” and Django templates to be the “views.” [...] Neither interpretation is more “correct” than the other. The important thing is to understand the underlying concepts.

This sounds like a subtle but possibly important distinction, particularly as I move between frameworks. I have some initial concerns about Django's interpretation of MVC but I'll keep that to myself until I've really given it time to make sense (basically, how does the split of business logic between Django "model" and "view" manifest itself in the design of your code, and can it lead to anemic domain models?).

Why Django?

Behind the 8-ball here. Not only is Django new to me but Python isn't a language I code in regularly -- in fact it's been some time since I've played with it. I like the look of Python. I've coded some trivial programs with it. The "white space thing" doesn't bother me and I don't really understand why it would bother anyone. Then again it's not the first language I've seen that does it. The first language that I saw that particular feature in was Occam, and I really liked Occam (not that I ever did anything useful with it).

So why Django?

• It's based on Python and Python seems like it should be a really good language to work in. I'm a Perl refugee in some ways. I'm finding it hard to recruit really good Perl coders (as opposed to just plain old Perl coders) and I suspect that people who have taken the trouble to learn Python (or Ruby, or Scala, or LISP) are more likely to care about good code. Not because C# and Java programmers don't but ... well, in this market why would you learn Python if it wasn't because you cared about being a better programmer?

• There are other Python frameworks that look very interesting: TurboGears and Pylons for example. But I have limited time and Django appears to have an edge for reasons I can't yet articulate. I'll probably drill down into TurboGears later.

• Django is the first framework supported by Google App Engine.

• The Django core team say sensible things about web development and the community appears active and supportive. A little smug sometimes but hey, wouldn't you be, if you were working in the One True Language too? :-)

Notes on "Mental Detox"

So apparently of three that set out I was the only one to make it to Friday, which is not even a full week. For shame Kate, for shame. :-)

In the 5 days during my self imposed personal net exile:

• I clocked up a modest amount of spam (219 messages), mailing list messages (184 conversations) and personal e-mail.
• There were 634 RSS items in Google Reader.
• There were 19 podcasts downloaded by iTunes.

And I learned:

• That I don't miss, like or need Facebook. But it seems rude to delete my account...
• That I follow far too many total freakin' strangers on Twitter. I need some Twitter Equilibrium :-)
• I have too many RSS feeds that don't really tell me anything I need to know.

Well. Just some random notes from no-one of consequence. Seriously, why are you reading this?

Mental Detox Week (redux)

Mental Detox week was 21 - 27 April but I missed it completely (despite being an Adbusters subscriber). So Kate Carruthers and some of her friends (including me) are doing a Mental Detox week from May 12 to 17. Which isn't actually a full week but baby steps people, baby steps.

Given that I'll still be working I'll still need to use a computer. But

• No IM
• No personal e-mail
• No Facebook (that one will be easy)
• No iPod (that one will be hard)
• No TV, radio or Google Reader.
  
• And no Twitter.

Don't watch TV anyway and the radio sucks but not sure what the policy is on the print version of newspapers. Not reading my RSS feeds in Google Reader leaves me with the feeling that I might "miss something." What if they announce the next Google App Engine next week? On the other hand, real news can put that kind of event into perspective.

In hindsight it was pointless to commit to this during a working week. There's still an awful lot of noise to deal with at work. Next time I'll try this kind of electronic-blackout during annual leave but I'm committed now so...

See you in a week. :-)

About the Application

The application is going to be small "to do" app loosely based on David Allen's Getting Things Done. Not that the world needs another "to do" app (or even another GTD app) but it fits the basic criteria: it's small but not trivial, capable of being built in a few days and the problem is well understood enough that I can concentrate on learning the basics of the framework rather than solving some other problem.

Here's a short summary of the requirements:

• Users need to be able to register with a user name and password to save and access their lists. The "stretch target" would be to allow users to start making lists anonymously, and then to save that work upon registering. If they already have an account, then the anonymous list and previously saved list should be merged sensibly.
• Users will make lists of tasks. So we have the concept of a "list" (users must have at least one). A list should have a name and, when users are looking at the "list of lists" should be able to be sorted arbitrarily (in other words, users should be able to force a particular list to the "top" or above another list).
• Lists contain tasks. A task needs a name, some notes, and the same sorting behaviour as lists (ie give users full control over the order of the list).
• Each task can have exactly one context. A context is a GTD concept -- it's basically the things you need to get a task done. Example context might be "at work", "at home", "online" -- so that a task that has the context "at work" is something to do at work. Each user can have their own set of unique contexts but it's expected that the application will provide some sensible defaults.
• Stretch target: Allow tasks to have an arbitrary number of contexts which represent the intersection of those requirements. A task that has the context "home" and "online" is one that requires an Internet connection from home to do. Not very "GTD-y" to make things overly complex though...
• There is the concept of a context being "current." In other words, you tell the application "I am at work" and it will only show you the "at work" tasks.
• Stretch target: When a user logs on, the default context should be the last context they were using from that particular device. For example, if they've logged on from their iPhone and have set their current context to "errands" then the next time they log on from their iPhone that should be the default context. However, if they log on from work immediately after, the default context will be "at work." It is anticipated that the browser string will be unique enough for this.
• Stretch target: Mobile and Twitter support.

So, there you have it. Will not set the world on fire but I'm confident that we can get to know some of the frameworks well enough to get a "feel" for how they see the problem and how much code it takes to get it going.

I shall call it "lulztodo", because we're doing it for the lulz (thanks Nick).

Method and Approach to the Evaluation

I think we learn best by doing. I learn best by doing. So I'm going to attempt to build an application in some of the frameworks I'm looking at.

The application will need to be

• Small: Nothing too fancy -- the point is to learn a little about web development with a given framework, not solve an actual real problem. That will come later.
• Well understood: In order to concentrate on learning the framework, I'm not going to try and solve the Travelling Salesman problem in O(1) time.
• Non-trivial: Despite the above, it will need to be a bit more fancy than "Hello World." It should require persistent data storage, authentication and do something vaguely useful.

So, if I develop the same application over and over again in different frameworks each time I hope to get roughly comparable results.

Searching for the One True Framework

No, I don't really believe there is One True Framework. But I am thinking about future web architecture directions for our group.

I'm going to write a series of posts comparing and contrasting a few different languages and framework combinations. These frameworks seem to be emerging as leaders in their language / platform niche:

• Django (Python)
• Catalyst (Perl)
• CakePHP (PHP)
• Rails (Ruby)
• Wicket (Java)
• Grails (Groovy)

That list in no particular order by the way. I don't think I could sensibly look at all of them or do them justice. And it might be smarter to pick a language first and then evaluate the frameworks available for it. But at this stage I'm going for "breadth" first and then I'll drill down into more detail.

About this Blog

Purpose and Function

To aid memory.

What is a "Hissohathair?"

 I do not know.

The origin of the name comes from some graffiti scrawled on a few walls in what was my home suburb of Enmore  (Sydney, Australia). It was variously written as "hisso hathair", "his so hat hair", and "hiss ho hat hair."

I never did find out what that meant. But it was amusing (to me), unique (and therefore registrable) and opaque.

[Note: This post was edited after it was first published, to add the explanation for the blog's name.]

Who are you?

Who are you?

No-one of consequence.

I must know!

Get used to disappointment.

;-)