Problems with Custom Tag Filter

[Mark Phillips]

I have a dictionary of dictionaries that I need to open up in a template.

The dictionary:

'values': {(1L, 2L): {'selling_costs__sum': None, 'sale_price__sum': None, 'debt__sum': None, 'estimate__quote__sum': None}, 

(3L, 2L): {'selling_costs__sum': Decimal('10.45'), 'sale_price__sum': Decimal('50.00'), 'debt__sum': Decimal('0.00'), 'estimate__quote__sum': Decimal('100.00')}}

My templatetag:

from django import template

register = template.Library()

@register.filter

def lookup(container, key):

    if type(container) is dict:

        return container.get(key)

    elif type(container) in (list, tuple):

        return container[key] if len(container) > key else None

    return None

And my template code:

{% for location in locations %}

    {% for category in categories %}

<tr>

    <td>{{ location }}</td>

    <td>{{ category }}</td>

    <td>${{ values|lookup:(location.id, category.id)|lookup:'selling_costs__sum' }}</td>

</tr>

    {% endfor %}

{% endfor %}

The error I get is: lookup requires 1 arguments, 0 provided.

The location.id and category.id both generate the correct values. It seems that template tags can't take a tuple as a key for a dictionary. 

Also I read that one cannot chain a filter like this. Is this true?

Any suggestions on how to read data from the dictionary values?

Thanks!

Mark