Django Node AttributeError

Question

I'm in the process of learning Django and I'm currently stuck at creating my own template tags. I'm trying to create something that would create a menu based on a string with menu items. In Django template language, the following would produce what I'm looking for:

{% for item in menu_items %}

{{ item }} {% if not forloop.last %} | {% endif %}

{% endfor %}

Here's what I try to input in a designated templatetags application:

def construct_menu(parser, token):
  try:
    tag_name, menu_items = token.split_contents()
  except ValueError:
    msg = '%r tag requires a space separated quote of strings.' % token.split_contents()[0]
    raise template.TemplateSyntaxError(msg)
  return MenuNode(menu_items[1:-1])

class MenuNode(template.Node):
  def __init__(self, menu_items):
    self.menu_items = str(self.menu_items)

  def render(self, context):
    ...

register.tag('menu', construct_menu)

And here's the error that I get:

Environment:


Request Method: GET
Request URL: http://127.0.0.1:8000/news/

Django Version: 1.5.1
Python Version: 2.7.2
Installed Applications:
('django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.sites',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'news',
 'showroom',
 'contact',
 'templatetags')
Installed Middleware:
('django.middleware.common.CommonMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware')


Template error:
In template /Users/per/Documents/Tilde/templates/home.html, error at line 1
   'MenuNode' object has no attribute 'menu_items'
   1 :  {% extends "base.html" %} 


   2 : 


   3 : {% block title %}


   4 :   Home page! :D


   5 : {% endblock %}


   6 :   for post in posts


   7 :     post


   8 :   endfor  


   9 : {% block content %}


   10 : This is where the news goes. 


   11 : {% endblock %}

Traceback:
File "/Library/Python/2.7/site-packages/django/core/handlers/base.py" in get_response
  115.                         response = callback(request, *callback_args, **callback_kwargs)
File "/Users/per/Documents/Tilde/news/views.py" in home
  6.   return render(request, 'home.html')
File "/Library/Python/2.7/site-packages/django/shortcuts/__init__.py" in render
  53.     return HttpResponse(loader.render_to_string(*args, **kwargs),
File "/Library/Python/2.7/site-packages/django/template/loader.py" in render_to_string
  177.         return t.render(context_instance)
File "/Library/Python/2.7/site-packages/django/template/base.py" in render
  140.             return self._render(context)
File "/Library/Python/2.7/site-packages/django/template/base.py" in _render
  134.         return self.nodelist.render(context)
File "/Library/Python/2.7/site-packages/django/template/base.py" in render
  830.                 bit = self.render_node(node, context)
File "/Library/Python/2.7/site-packages/django/template/debug.py" in render_node
  74.             return node.render(context)
File "/Library/Python/2.7/site-packages/django/template/loader_tags.py" in render
  102.         compiled_parent = self.get_parent(context)
File "/Library/Python/2.7/site-packages/django/template/loader_tags.py" in get_parent
  99.         return get_template(parent)
File "/Library/Python/2.7/site-packages/django/template/loader.py" in get_template
  146.     template, origin = find_template(template_name)
File "/Library/Python/2.7/site-packages/django/template/loader.py" in find_template
  135.             source, display_name = loader(name, dirs)
File "/Library/Python/2.7/site-packages/django/template/loader.py" in __call__
  43.         return self.load_template(template_name, template_dirs)
File "/Library/Python/2.7/site-packages/django/template/loader.py" in load_template
  49.             template = get_template_from_string(source, origin, template_name)
File "/Library/Python/2.7/site-packages/django/template/loader.py" in get_template_from_string
  157.     return Template(source, origin, name)
File "/Library/Python/2.7/site-packages/django/template/base.py" in __init__
  125.         self.nodelist = compile_string(template_string, origin)
File "/Library/Python/2.7/site-packages/django/template/base.py" in compile_string
  153.     return parser.parse()
File "/Library/Python/2.7/site-packages/django/template/base.py" in parse
  274.                     compiled_result = compile_func(self, token)
File "/Users/per/Documents/Tilde/templatetags/templatetags/tagtest.py" in construct_menu
  34.     return MenuNode(menu_items[1:-1])
File "/Users/per/Documents/Tilde/templatetags/templatetags/tagtest.py" in __init__
  38.         self.menu_items = str(self.menu_items)

Exception Type: AttributeError at /news/
Exception Value: 'MenuNode' object has no attribute 'menu_items'

I'm basically copying the entire thing from http://www.djangobook.com/en/2.0/chapter09.html, but this error doesn't make sense to me. I think I pass all the valid attributes to the relevant places. Any advice?

Many thanks in advance!

Answer 1

The traceback shows you that the error occurs here:

self.menu_items = str(self.menu_items)

But this is the first line of the __init__ method. self.menu_items doesn't exist yet, because you haven't assigned it. I expect you mean:

self.menu_items = str(menu_items)

(although, since you're presumably going to iterate through menu_items at some stage, I'm not sure why you want to convert it to a string).