Django templates and variable attributes

Question

I'm using Google App Engine and Django templates.
I have a table that I want to display the objects look something like:

Object Result: Items = [item1,item2] Users = [{name='username',item1=3,item2=4},..]

The Django template is:

<table> <tr align="center"> <th>user</th> {% for item in result.items %} <th>{{item}}</th> {% endfor %} </tr> {% for user in result.users %} <tr align="center"> <td>{{user.name}}</td> {% for item in result.items %} <td>{{ user.item }}</td> {% endfor %} </tr> {% endfor %} </table>

Now the Django documention states that when it sees a . in variables
It tries several things to get the data, one of which is dictionary lookup which is exactly what I want but doesn't seem to happen...

This is an elegant solution : stackoverflow.com/a/8000091/781695 — user
– user, Commented Apr 11, 2014 at 18:32

Yon · Accepted Answer · 2008-09-08 19:01:24Z

I found a "nicer"/"better" solution for getting variables inside Its not the nicest way, but it works.

You install a custom filter into django which gets the key of your dict as a parameter

To make it work in google app-engine you need to add a file to your main directory, I called mine django_hack.py which contains this little piece of code

from google.appengine.ext import webapp register = webapp.template.create_template_register() def hash(h,key): if key in h: return h[key] else: return None register.filter(hash)

Now that we have this file, all we need to do is tell the app-engine to use it... we do that by adding this little line to your main file

webapp.template.register_template_library('django_hack')

and in your template view add this template instead of the usual code

{{ user|hash:item }}

And its should work perfectly =)

David Webb · Accepted Answer · 2008-08-30 14:22:52Z

I'm assuming that the part the doesn't work is {{ user.item }}.

Django will be trying a dictionary lookup, but using the string "item" and not the value of the item loop variable. Django did the same thing when it resolved {{ user.name }} to the name attribute of the user object, rather than looking for a variable called name.

I think you will need to do some preprocessing of the data in your view before you render it in your template.

Martyn · Accepted Answer · 2010-08-12 09:36:35Z

Or you can use the default django system which is used to resolve attributes in tempaltes like this :

from django.template import Variable, VariableDoesNotExist @register.filter def hash(object, attr): pseudo_context = { 'object' : object } try: value = Variable('object.%s' % attr).resolve(pseudo_context) except VariableDoesNotExist: value = None return value

That just works

in your template :

{{ user|hash:item }}

Brandon Henry · Accepted Answer · 2009-08-14 15:45:39Z

@Dave Webb (i haven't been rated high enough to comment yet)

The dot lookups can be summarized like this: when the template system encounters a dot in a variable name, it tries the following lookups, in this order:

* Dictionary lookup (e.e., foo["bar"]) * Attribute lookup (e.g., foo.bar) * Method call (e.g., foo.bar()) * List-index lookup (e.g., foo[bar])

The system uses the first lookup type that works. It’s short-circuit logic.

Niall Farrington · Accepted Answer · 2010-06-27 00:34:47Z

As a replacement for k,v in user.items on Google App Engine using django templates where user = {'a':1, 'b', 2, 'c', 3}

{% for pair in user.items %} {% for keyval in pair %} {{ keyval }}{% endfor %}<br> {% endfor %}

a 1
b 2
c 3

pair = (key, value) for each dictionary item.

Martijn Pieters · Accepted Answer · 2012-11-14 11:01:56Z

0

shouldn't this:

{{ user.item }}

be this?

{{ item }}

there is no user object in the context within that loop....?

edited Nov 14, 2012 at 11:01

Martijn Pieters

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answered Aug 31, 2008 at 22:29

Nic Wise

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