django: Easy way for template tags to add information to template context

I've been seeing a pattern emerging with Django template tags that I've been writing and it's starting to annoy me.

Example usage:

view sourceprint?

1.{% some_tag by request.user as context_var %}  

2.{% for item in context_var %} ... {% endfor %}

The template tag would be:

view sourceprint?

01.from django.template import Library, Node, Variable

02. 

03.register = Library()

04. 

05.@register.tag

06.def some_tag(parser, token):

07.  bits = token.split_contents()

08.  tag = bits.pop(0) # pop tag

09.  context_var = None

10. 

11.  if len(bits):

12.    context_var = bits.pop(0)

13. 

14.  user_var = Variable(bits.pop())

15.  return SomeTagNode(context_var, user_var = user_var)

16. 

17.class SomeTagNode(Node):

18.  def __init__(self, context_var, user_var = None):

19.    self.context_var, self.user_var = context_var, user_var

20. 

21.  def render(self, context):

22.    context[self.context_var] = SomeModel.objects.filter(user = self.user_var.resolve(context))

23.    return ''

As you can see, there is some fluffing involved with creating a new class for something that could be done easily. The trick is finding a way to make it easier to re-use.

I found it annoying that registering tags using Library.simple_tag() automatically parses the context values (but did not allow access to it) and Library.inclusion_tag() supported the use of takes_context but the regular Library.tag() didn't.

Place this code in a re-usable file.

view sourceprint?

1.from django.template import Node

2. 

3.class ContextNode(Node):

4.  def __init__(self, func):

5.    self.func = func

6. 

7.  def render(self, context):

8.    return self.func(context)

Now if you want to create a new tag:

view sourceprint?

01.from django.template import Library, TemplateSyntaxError, resolve_variable

02. 

03.register = Library()

04. 

05.@register.tag

06.def some_tag(parser, tokens):

07.  bits = token.split_contents()

08.  tag = bits.pop(0) # pop tag

09.  context_var = None

10. 

11.  if len(bits):

12.    context_var = bits.pop(0)

13. 

14.  user_var = bits.pop()

15. 

16.  # This is a wrapper function to accept the context variable

17.  def some_tag_wrap(context):

18.    context[context_var] = SomeModel.objects.filter(user = resolve_variable(user_var, context))

19.    return ''

20. 

21.  return ContextNode(some_tag_wrap)

This makes life much simpler if all you want to do is add a variable to the context.

Also, note the use of resolve_variable(), which gets rid of the repetitively annoying use of Variable.resolve().

Now you can go back to doing things in life that matter.