python - *args, **kwargs in jinja2 macros

Question

How are extra args & kwargs handled for a Jinja2 macro? The documentation isn't exactly clear offhand.

For example, this is clearly wrong:

{% macro example_1(one, two, **kwargs) %}
    do macro stuff
{% endmacro %}

which results in

jinja2.exceptions.TemplateSyntaxError

TemplateSyntaxError: expected token 'name', got '**'

The documentation says:

kwargs

Like varargs but for keyword arguments. All unconsumed keyword arguments are stored in this special variable.

Unfortunately, any combo of extra keyword arguments is an error,

{% macro example_2(one, two) %}
    do macro stuff
{% endmacro %}

{{ example_2(one, two, test='test') }}

TypeError: macro 'example_2' takes no keyword keyword argument 'test'

I have no examples and am not poking about in the Jinja2 source code atm. The documentation isn't clear to me at this point. Any thoughts appreciated.

Answer 1

The trick is that kwargs has to be accessed at least once in any macro that should accept them. That is to say, you must call {{ kwargs }} once in macro body without declaring it in macro argument list. The same is true for {{ varargs }}.

This will not work

{% macro example_2(one, two) %}
    * {{one}} - {{two}}
{% endmacro %}
{{example_2(1, 2, test="Hello")}}

This will

{% macro example_2(one, two) %}
    * {{one}} - {{two}}
    * {{kwargs}}
{% endmacro %}
{{example_2(1, 2, test="Hello")}}