How to make 2 FOR loops in Dajngo2 templates?

Question

Django

How to make 2 FOR loops in templates? I do

{% for country in country_list %}
    <li>{{ country.grouper }}
    <ul>
        {% for city in country.list %}
          <li>{{ city.name }}: {{ city.population }}</li>
        {% endfor %}
    </ul>
    </li>
{% endfor %

I also throw one loop into another, but at the same time, the nested loop works only once and that's it ...