How to Write Django Template Tags

Template tags can be useful for making your applications more reusable by other projects. For this example I will be adding to the . Also, I’ve bundled the .

Start off by creating a folder called templatetags in your app directory and create two files in it. The first one named __init__.py and the second book_tags.py. There’s 3 things that we need to accomplish with our template tags. The first is to create a tag that will output the url for the action of the form. For example, {% get_book_form_url foo_object %}Next we need to get the form and assign it to a template variable that can be specified by the template variable. For example, {% book_form as bar_var %}. And the third template tag will get the books for an object and place in a template variable. For example, {% books_for_object foo_object as bar_var %}.

from django.template import Library, Node, TemplateSyntaxError
from django.template import Variable, resolve_variable
from django.utils.translation import ugettext as _
from django.contrib.contenttypes.models import ContentType
from django.core.urlresolvers import reverse
from books.models import Book
 
register = Library()
 
def get_contenttype_kwargs(content_object):
    """
    Gets the basic kwargs necessary for form submission url
    """
    kwargs = {'content_type_id':
        ContentType.objects.get_for_model(content_object).id,
    'object_id':
        getattr(content_object, 'pk',
            getattr(content_object, 'id')),
    }
    return kwargs
 
def get_book_form_url(content_object):
    """
    prints url for form action
    """
    kwargs = get_contenttype_kwargs(content_object)
    return reverse('new_book', kwargs=kwargs)
 
class BooksForObjectsNode(Node):
    """
    Get the books and add to the context
    """
    def __init__(self, obj, context_var):
        self.obj = Variable(obj)
        self.context_var = context_var
 
    def render(self, context):
        content_type = ContentType.objects.get_for_model(
            self.obj.resolve(context))
        # create the template var by adding to context
        context[self.context_var] = \
            Book.objects.filter( # find all books for object
                content_type__pk = content_type.id,
                object_id = self.obj.resolve(context).id
            )
        return ''
 
def books_for_object(parser, token):
    """
    Retrieves a list of books for given object
    {% books_for_object foo_object as book_list %}
    """
    try:
        bits = token.split_contents()
    except ValueError:
        raise TemplateSyntaxError(
            _('tag requires exactly two arguments')
    if len(bits) != 4:
        raise TemplateSyntaxError(
            _('tag requires exactly three arguments')
    if bits[2] != 'as':
        raise TemplateSyntaxError(
            _("second argument to tag must be 'as'")
    return BooksForObjectsNode(bits[1], bits[3])





 
def book_form(parser, token):
    """
    Adds a form to the context as given variable
    {% book_form as form %}
    """
    # take steps to ensure template var was formatted properly
    try:
        bits = token.split_contents()
    except ValueError:
        raise TemplateSyntaxError(
            _('tag requires exactly two arguments')
    if bits[1] != 'as':
        raise TemplateSyntaxError(
            _("second argument to tag must be 'as'")
    if len(bits) != 3:
        raise TemplateSyntaxError(
            _('tag requires exactly two arguments')
    # get the form
    return BookFormNode(bits[2])
 
class BookFormNode(Node):
    """
    Get the form and add it to the context
    """
    def __init__(self, context_name):
        self.context_name = context_name
    def render(self, context):
        from books.forms import NewBookForm
        form = NewBookForm()
        # create the template var by adding to context
        context[self.context_name] = form
        return ''
 
# register these tags for use in template files
register.tag('books_for_object', books_for_object)
register.tag('book_form', book_form)
register.simple_tag(get_book_form_url)

Add this to your template

To start adding books to an object, add this code to your template and change my_awesome_object_here to the template variable name of your object.

Books
{% load book_tags %}
 
{% books_for_object my_awesome_object_here as books %}
{% for book in books %}
 
{{ book }} -
        {{ book.description }}
 
{% endfor %}
Add a book

{% book_form as form %}
{{ form }}

You can get the template tags source code and the code from at the or by doing

svn co  books

in a directory on the python path.