Multiple blocks of same name in Jinja2

Question

In Jinja2, I have a base template like this:

<title>{% block title %}{% endblock %} - example.com</title>
[...]

<h1> 
  {% block title %}{% endblock %} - example.com
</h1>

Jinja2, then, fails with the following message:

  lines = [self.message, '  ' + location]
: block 'title' defined twice

It must be now evident as to what I am trying to do - to have the same title in two places: the TITLE tag and the H1 tag, but the part of the title is actually provided by other derived templates.

How does one typically achieve this?

Answer 1

As documented here, defining a block creates a macro with the name of the block in the special "self" object:

<title>{% block title %}{% endblock %} - example.com</title>
[...]

<h1> 
  {{ self.title() }} - example.com
</h1>

Answer 2

The idea is to create a block inside a macro and then call macro two times, instead of having "block" tag repeated twice.

In latest Jinja2 version this works:

layout.html

{%- extends "base.html" -%}

{%- macro duplicated() -%}
    {% block overrideninchild %}{% endblock %}
{%- endmacro -%}

{% block base_content %}
    {{ duplicated() }}
    {{ duplicated() }}
{% endblock %}

child_page.html

{%- extends "layout.html" -%}

{% block overrideninchild %}
   Should be visible twice.
{% endblock %}