How can I check the size of a collection within a Django template?
See https://docs.djangoproject.com/en/stable/ref/templates/builtins/#if : just use, to reproduce their example:
{% if athlete_list %} Number of athletes: {{ athlete_list|length }}{% else %} No athletes.{% endif %}
If you're using a recent Django, changelist 9530 introduced an {% empty %} block, allowing you to write
{% for athlete in athlete_list %} ...{% empty %} No athletes{% endfor %}Useful when the something that you want to do involves special treatment for lists that might be empty.
A list is considered to be False if it has no elements, so you can do something like this:
{% if mylist %} <p>I have a list!</p>{% else %} <p>I don't have a list!</p>{% endif %}