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.

Answer 1

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 %} 

Answer 2

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...