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…

Asked By: Yon

||

Source

Answer 1

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.

Answered By: Dave Webb

Answer 2

shouldn’t this:

{{ user.item }}

be this?

{{ item }}

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

Answered By: Nic Wise

Answer 3

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 =)

Answered By: Yon

Answer 4

@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.

Answered By: Brandon Henry

Answer 5

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.

Answered By: Niall Farrington

Answer 6

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 }}

Answered By: Martyn

Django templates and variable attributes

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