It’s very useful when you want to display the last news in the first page of your website, but don’t want it to break if there isn’t one to show. It’s just a use case for such a code, but there are many more.

In the past I used to write something like this:

try:
    first_user = User.objects.all()[:1][0]
except IndexError:
    first_user = None

This is four lines to do a very simple task and I wanted to evolve this to use only one line of code. So I developed a function that do this to me. It’s inspired in the django.shortcuts.get_object_or_404. Let’s take a look at the code:

def get_first_object_or_none(queryset):
    try:
        return queryset[:1][0]
    except IndexError:
        return None

I’ve put this code in a module called shortcuts inside my project and now everytime I want to use it I can write this code:

from shortcuts import get_first_object_or_none
first_user = get_first_object_or_none(User.objects.all())

I think it’s a very good result and helps a lot in my coding. It also made my code more legible and easy to understand. It increased my productivity and I am publishing to increase others productivity also. Any doubts, questions os suggestions, please leave a comment.

Venho através deste convidá-los ao FLISOL/RN 2009. O Festival Latino-americano de Instalação de Software Livre do RN irá acontecer no dia 25 de abril de 2009 no SENAC em Natal.

No evento eu irei ministrar um mini-curso introdutório ao framework Django das 14:00 as 17:00 horas, cujo objetivo é formar pessoas com conhecimentos básicos acerca do framework. O mini-curso irá abordar diversos conceitos do django através do desenvolvimento de um blog.

Maiores informações sobre o evento podem ser encontradas no site.

In sphinx-quickstart command, it asks if you want to add this extension. If so, It adds this code to your conf.py file:

extensions = ['sphinx.ext.intersphinx']
intersphinx_mapping = {'http://docs.python.org/dev': None}

As you can see, it comes integrated with python documentation by default. But what I want is to integrate with Django documentation. So I changed the code a little bit:

extensions = ['sphinx.ext.intersphinx']
intersphinx_mapping = {
    'http://docs.python.org/dev': None,
    'http://docs.djangoproject.com/en/dev': 'http://docs.djangoproject.com/en/dev/_objects',
}

Sphinx looks for default for the file name objects.inv inside the documentation root, but django doesn’t provide such a file. Since ticket #10315 they provided a file like objects.inv but with a different URL: http://docs.djangoproject.com/en/dev/_objects/.

Now, all you have to do is reffer to classe or any kind of objects inside django: :class:django.contrib.auth.models.User. It will refference the User documentation inside django’s docs.

But it has a simple problem with Django, that I found the solution rlazo’s blog. But it still has some problems, when you are trying to document a pluggable app, that doesn’t have a project, you have to configure the django settings without the project settings, since pluggable apps doesn’t have a settings module.

Thanks to apollo13, who shown me this better approach, you can simply add this code to sphinx’s conf.py file:

from django.conf import settings
settings.configure()

With this approach, you don’t need to add any kind of fake files in your project.

The default HTTP 500 handler in django uses Context instead of RequestContext. It means that none of your template context processors will be loaded, and the MEDIA_URL variable available in the template system comes exactly from one of these processors. So, without template context processors, we get no MEDIA_URL variable in templates.

Searching in google for a solution to this problem I found a snippet[1] that solves the MEDIA_URL problem. But it still doesn’t load the processors, all it does is pass the MEDIA_URL variable to the context for template. So I decided to make simple changes in it to load the processors. And here is the complete code:

def server_error(request, template_name='500.html'):
    from django.template import RequestContext
    from django.http import HttpResponseServerError
    t = loader.get_template(template_name)
    return HttpResponseServerError(t.render(RequestContext(request)))

Put this code in any views file you want and then define it as the handler500 in your urls.py:

handler500 = 'views.server_error'

[1] http://www.djangosnippets.org/snippets/1199/

Before this update, queryset could be filtered only by absolute values.

queryset.filter(field='absolute value')

Will generate somthing like this:

SELECT * FROM table_name WHERE field = 'absolute value';

Now you can filter by another’s table field value.

queryset.filter(field=F('another_field'))

Will generate something like this:

SELECT * FROM table_name WHERE field = another_field;

The feature also supports arithmetical operations in the lookups so you can do filters where the views_number is twice as big as the comments_number.

queryset.filter(views_number__gt=F('comments_number')*2)

Will generate a SQL like this:

SELECT * FROM table_name WHERE views_number = comments_number*2;

It’s a very good feature. So, checkout the SVN version and take a look at docs/topics/db/queries.txt to know more about this.

All you have to do is create a folder named locale inside your app’s folder and run the command django-admin.py makemessages -l <your-locale> and it will create the file for you. To compile the messages, use the command django-admin.py compilemessages -l <your-locale>

That’s it, as simple as everything in django.

Here is the official documentation of this feature: http://docs.djangoproject.com/en/dev/topics/db/aggregation/

{% load mytemplatetags %}

It was much better if you just use the filters, without the need to load it. The reason you have to load is to achieve a better performance. But there’s a function of the template module called add_to_builtins that solves this problem. You can easily define a template tag or filter as builtin and use it like the builtin django template tags and filters. Just put this code in a file that is loaded ever, like the init.py of your project.

from django.template import add_to_builtins
add_to_builtins('path.to.templatetags.file')

Where ‘path.to.templatetags.file’ is the path of the file containing the template tags. For example, I have an app, inside my project, named mytagsapp. Inside this app I have the module templatetags with a file named mytags.py with my custom tags. So I will have to call add_builtins(‘mytagsapp.templatetags.mytags’). My project folder should look like this:

Folders structure

Make sure your app is in the INSTALED_APPS setting in your settings.py project. It will guarantee that the init.py of you app will get called. So just put the code above in this file (red in image).

Remember to not use this feature with all your template filters as it will mean loss of performance.