Question

I’ve developed a custom i18n system in Jinja2 based on the following filter (simplified):

@contextfilter
def render(context, value):
    """
    Renders the filtered value as a string template, using the context
    and environment of the caller template.
    """
    mini_template = _environment.from_string(value)
    return mini_template.render(context)

This allows me, for example, to create the following context:

context = {
    'user': {
        'name': 'Joel',
        'locale': 'es'
    }
    'greetings': {
        'en': 'Hi {{user.name}}!',
        'es': '¡Hola {{user.name}}!'
    }
}

And use it like this in my templates:

{{ greetings[user.locale]|render() }}

That works perfectly.

Now imagine that I’ve an array of users instead of a single one. I was doing the following in Django Templates, but it doesn’t work in Jinja2 because the variable ‘user’ is not in the context:

{% for user in list_of_users %}
    {{ greetings[user.locale]|render() }}
{% endfor %}

Is there anything I could do to add the new variable (user) to the context I use at the contextfilter? I need to add both its name and value if I want it to work.

Thank you very much for your help.

Answer 1

Ok, I’ve fixed it using kwargs (although it’s more verbose than its equivalente in Django templates).

Filter:

@contextfilter
def render(context, value, **kwargs):
    """
    Renders the filtered value as a string template, using the context
    and environment of the caller template.
    """
    if kwargs:
        kwargs.update(context)
        ctx = kwargs
    else:
        ctx = context

    #we render the string as its own template
    mini_template = _environment.from_string(value)
    return mini_template.render(ctx)

Usage:

{% for user in list_of_users %}
    {{ greetings[user.locale]|render(user=user) }}
{% endfor %}