Let's say there are base_a.html, base_b.html, a.html, b.html, c.html.
a.html extends base_a.html and b.html extends base_b.html.
And c.html has to extend both base_a.html and base_b.html.
It will be easier to understand this situation if you think base_a.html contains reply functionalities and base_b.html contains search functionalities.
Can I use multiple inheritance in Django template?
Or do I have to use include instead of extends?
As stated at the docs,
If you use
{% extends %}in a template, it must be the first template tag in that template.
That suggests that an {% extends %} tag cannot be placed in the second line, that is, you cannot have two {% extends %} tags.
Your case can easily be solved with {% include %} tags. For example:
In a.html:
{% include 'base_a.html' %}
In b.html:
{% include 'base_b.html' %}
In c.html:
{% include 'base_a.html' %}
{% include 'base_b.html' %}
Of course, base_a.html and base_b.html should only contain the specific block you want to reuse, not a full HTML template.