The value of conventions, aka testmaker for template tags.

A couple posts ago, I talked about how we should have conventions for the names that we use in Django Template Blocks. Today I will be talking about the value that is gained from this kind of structure.

Use Cases

Template Tags

My use case for Template tags is what started me thinking about this. Some of you may know that I have created a testmaker application for Django. This allows you to automatically test your view code, based on a browser session. Once I got most of the kinks worked out in this code, I started thinking about what the next best thing to test would be. I came up with template tags...

This is where I ran into a problem. With no context associated with a template tag, there is no way to create a tool which tests template tags well. At first I simply started out trying to test the template tags by pulling them out of the template verbatim.

{% load blog %}{% get_latest_posts for as posts limit 10 %}

However, when you try and test this, it doesn’t work. That is because all this code is doing is settings a context variable, and not outputting anything. You can create tests for trivial template tags that just output a string, but a lot of template tags set context variables. So without some kind of convention here, it is impossible to write a tool that will automatically write a test for you. That sucks!

Luckily in Django, the above test is representative of a kind of convention in django template tags. Most template tags use the syntax as [context_var] to set a variable in the context. So I went ahead and wrote some code that parses template tags for these kind of strings.

This code is valuable for some people, but is worthless if people use another syntax for defining context variables. This I think is a really good example of where syntax (or convention) allow you to do more than you previously could.

You can take a look at the source code here. It’s still a bit rough, like most of my first releases it is more of a proof of concept.

Template Blocks

So if we create a convention for Template blocks like I proposed in my previous post, this gives us some really neat possibilities. We can now create a base template that “knows” what will be included in each of it’s sections. So in turn we create a way to provide skins or themes for Django Sites, that would be portable between Installations.

Of course, how far we take these conventions will limit how portable, powerful, and easy to replicate the designs will be. If we say that all items in a menu block have to be <ul class=menu_item>, then we can provide more functionality in our portable base template. This is a bit too specific though, because not all menus are lists. However, even with just a simple structure around your base template, you can create some really nice portable templates. You can create 1 and 2 column layouts, simply based on where the menu, content, header, and footer are for example.

I think it will be interesting seeing where we can embrace conventions where possible, for the betterment of all. I think that having Django Skins would be really neat :). Also, having tests automagically generated for template tags is a big win. For no other reason than because it does the boilerplate stuff for you.

Other places

I think that there are more places where conventions could benefit us. I think I’m going to create a section in my projects on this site dedicated to conventions for Django. Hopefully serving as a reference for other people who are trying to use conventions in their Django apps.

Hey there. I'm Eric and I do consulting and provide other services around software documentation. Feel free to email me if you want to chat.