*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.

Asked By: blueblank

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Source

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")}}

Answered By: Sean Vieira

Answer 2

Just to add to Sean Viera’s answer, the kwargs object will be a dictionary so if you want to use it you can iterate over it by accessing the items() method, like in normal Python:

{% macro iterate_kwargs() %}
    {% for key, value in kwargs.items() %}
    The key, {{ key }}, has a value of {{ value }}
    {%- endfor -%}
{% endmacro %}

{{ iterate_kwargs(id=123, colour="blue", size="S") }}

This will output the following:

    The key, id, has a value of 123
    The key, colour, has a value of blue
    The key, size, has a value of S

This was written and tested using dbt so may not be available to all tools that use Jinja

Answered By: Bill Wallis

*args, **kwargs in jinja2 macros

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