Django - How to do tuple unpacking in a template 'for' loop


Question

In my views.py, I'm building a list of two-tuples, where the second item in the tuple is another list, like this:

[ Product_Type_1, [ product_1, product_2 ],
  Product_Type_2, [ product_3, product_4 ]]

In plain old Python, I could iteration the list like this:

for product_type, products in list:
    print product_type
    for product in products:
        print product

I can't seem to do the same thing in my Django template:

{% for product_type, products in product_list %}
    print product_type
    {% for product in products %}
        print product
    {% endfor %}
{% endfor %}

I get this error from Django:

Caught an exception while rendering: zip argument #2 must support iteration

Of course, there is some HTML markup in the template, not print statements. Is tuple unpacking not supported in the Django template language? Or am I going about this the wrong way? All I am trying to do is display a simple hierarchy of objects - there are several product types, each with several products (in models.py, Product has a foreign key to Product_type, a simple one-to-many relationship).

Obviously, I am quite new to Django, so any input would be appreciated.

1
55
11/7/2008 2:40:20 AM

Accepted Answer

it would be best if you construct your data like {note the '(' and ')' can be exchanged for '[' and ']' repectively, one being for tuples, one for lists}

[ (Product_Type_1, ( product_1, product_2 )),
   (Product_Type_2, ( product_3, product_4 )) ]

and have the template do this:

{% for product_type, products in product_type_list %}
    {{ product_type }}
    {% for product in products %}
        {{ product }}
    {% endfor %}
{% endfor %}

the way tuples/lists are unpacked in for loops is based on the item returned by the list iterator. each iteration only one item was returned. the first time around the loop, Product_Type_1, the second your list of products...

63
11/7/2008 8:45:17 PM

Another way is as follows.

If one has a list of tuples say:

mylst = [(a, b, c), (x, y, z), (l, m, n)]

then one can unpack this list in the template file in the following manner. In my case I had a list of tuples which contained the URL, title, and summary of a document.

{% for item in mylst %}    
     {{ item.0 }} {{ item.1}} {{ item.2 }}    
{% endfor %}

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