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.

Asked By: Chris Lawlor

||

Source

Answer 1

Just send the template a list of product types and do something like:

{% for product_type in product_type_list %}
    {{ product_type }}
    {% for product in product_type.products.all %}
        {{ product }}
    {% endfor %}
{% endfor %}

It’s been a little while so I can’t remember exactly what the syntax is, let me know if that works. Check the documentation.

Answered By: Harley Holcombe

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…

Answered By: Jake

Answer 3

You must used this way:

{% for product_type, products in product_list.items %}
    {{ product_type }}
    {% for product in products %}
       {{ product }}
    {% endfor %}
{% endfor %}

Don’t forget the variable items in the dictionary data

Answered By: Yasel

Answer 4

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 %}

Answered By: Ashwin Rao

Answer 5

If you have a fixed number in your tuples, you could just use indexing. I needed to mix a dictionary and the values were tuples, so I did this:

In the view:

my_dict = {'parrot': ('dead', 'stone'), 'lumberjack': ('sleep_all_night', 'work_all_day')}

In the template:

<select>
  {% for key, tuple in my_dict.items %}
    <option value="{{ key }}" important-attr="{{ tuple.0 }}">{{ tuple.1 }}</option>
  {% endfor %}
</select>

Answered By: famousfilm

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

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