Django: My context variable cannot be used for duplicate for loops

Question

In views.py I have the variable

mylist = zip(set1,set2,set3)

In templates I do

{% for val1, val2, val3 in mylist%}
{% endfor %}

It works fine. However, if I duplicate the condition it fails. Is it normal? Let's say I have the following:

# this is my page
some text
{% for val1, val2, val3 in mylist %}
  {{forloop.counter}}
{% endfor %}
more text
{% for val1, val2, val3 in mylist %}
  {{forloop.counter}}
{% endfor %}
more text
# final text of page

The first loop will work, and the second one will be empty. It seems as though I can only use once mylist. I didn't experience this issue with simple lists. One solution is to create 2 identical context variables to have 2 for loops but that seems odd...

Answer 1

Please note that…

The first line of code of your question is odd, I would replace it with:

myzip = zip(mylistA,mylistB,mytuple)

Indeed, a set() is iterable, but it doesn’t have any order. So using zip() in this case results in unexpected behaviour.

---

The answer

zip() returns an iterator. It can only be consumed once.

Try this as well in python:

myzip = zip([1,2,3], ("a","b","c"))

for i,j in myzip:
    print(i, j)

for i,j in myzip:
    print(i, j)

You’ll get the same behaviour. It will returns the following once:

1 a
2 b
3 c

A work-around is to call the list() function before any for loop:

mylist = list(myzip)