if..else custom template tag

Question

I'm implementing a custom permissions application in my Django project, and I'm lost as to how to implement a custom template tag that checks a logged in user's permissions for a specific object instance and shows a piece of HTML based on the outcome of the check.

What I have now is (pseudocode):

{% check_permission request.user "can_edit" on article %}
    <form>...</form>
{% endcheck %}

('check_permission' is my custom template tag).

The templatetag takes in the user, the permission and the object instance and returns the enclosed HTML (the form). This currently works fine.

What I would like to do however, is something like:

{% if check_permission request.user "can_edit" on article %}
    <form>...</form>
{% else %}
    {{ article }}
{% endif %}

I've read about the assignment tag, but my fear is that I would pollute the context variable space with this (meaning I might overwrite previous permission context variables). In other words, as the context variables are being defined on different levels (the view, middleware in my case, and now this assignment template tag), I'm worried about maintainability.

Answer 1

inside my_tags.py

from django import template
register = template.Library()

@register.simple_tag(takes_context=True)
def make_my_variable_true(context):
    context['my_variable'] = True
    return ''  # without this you'll get a "None" in your html

inside my_template.html

{% load my_tags %}
{% make_my_variable_true %}
{% if my_variable %}foo{% endif %}

Answer 2

You can use template filters inside if statements. So you could rewrite your tag as a filter:

{% if request.user|check_can_edit:article %}

Note that it's tricky to pass multiple arguments of different types to a filter, so you'll probably want to use one filter per permission, above I've used check_can_edit.