django template - parse variable inside string variable

Question

I'm pulling a dynamic content(from a database) to a template. You can think of this as some simple CMS system. The content string contains a template variable. Like this one (simplified case):

vars['current_city'] = "London"
vars['content'] = 'the current city is: {{current_city}}'  #this string comes from db
return render_template(request, 'about_me.html',vars)

then in template:

{{content}}

output obviously:
the current city is: {{current_city}}
expected:
the current city is: London

My question - is there any way to render a variable name inside another variable? Using custom template tag/filter seems to be a good idea but I was trying to create one with no success... Any ideas how this can be solved?

miki725 · Answer 1 · 2012-10-10T04:18:43.133

Having a custom tag can probably solve this issue, however it might get a little complicated because then there is a possibility of having a full template within a template since nothing restricts you from saving all of your templates in db (which might include other template tags). I think the easiest solution is to manually render the template string from the db, and then pass that as variable to the main template.

from django.template import Template, Context
...
context = {
    'current_city': 'London'
}
db_template = Template('the current city is: {{current_city}}') # get from db
context['content'] = db_template.render(Context(context))
return render_template(request, 'about_me.html', context)

Note:

If you do follow this road, this might not be very efficient since every time you will execute the view, the db template will have to be compiled. So then you might want to cache the compiled version of the db and then just pass the appropriate context to it. The following is very simple cache:

simple_cache = {}

def fooview(request):
    context = {
        'current_city': 'London'
    }
    db_template_string = 'the current city is: {{current_city}}'
    if simple_cache.has_key(db_template_string):
        db_template = simple_cache.get(db_template_string)
    else:
        simple_cache[db_template_string] = Template(db_template_string)
    context['content'] = db_template.render(Context(context))
    return render_template(request, 'about_me.html', context)

Thanks for this. Yes, on a view it's not that big issue as we have all the variables available. What if parsing can not be done inside a view? It would be ideal if we can have this content pulled out automatically for the current page, outside a view so we don't have to remember about it, in template context processor for example. Then we end up with a variable name in a string but how to access template variables in this case to render the string? — robertzp, Oct 10 '12 at 19:45

score 0 · Answer 2 · answered Jul 02 '22 at 17:43

To expand a bit on @miki725 answer:

You can create a simple template tag like this and have it render the django template logic with the context already present in the template:

from django.template import Context, Library, Template

library = Library()

@library.simple_tag(takes_context=True)
def render(context, string):
    template = Template(string)
    return template.render(context)

Use it like this:

{% render variable_with_template_logic %}

django template - parse variable inside string variable

2 Answers2

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