django 'if' statement improperly formatted

Question

Im getting strangest error in django so far:

'if' statement improperly formatted

Template that raises the error is this:

{% if diff >= 0 %}
<span class="pos">+{{ diff }}
{% else %}
<span class="neg">-{{ diff }}
{% endif %}
</span>
<span>{{ a }}</span>

view that has a and diff in context is this:

def add(request, kaart_id):
    if request.is_ajax() and request.method == 'POST':
        x = Kaart.objects.get(id=kaart_id)
        x.pos += 1
        x.save
        x = Kaart.objects.get(id=kaart_id)      
        from django.utils import simplejson
        diff = x.pos - x.neg
        a = "(+1)"
        context = { 'diff':diff, 'a':a }
        return render_to_response('sum.html', context, context_instance=RequestContext(request))

It does not matter what equation i use in if, >, >=, ==.. they all raise the same error.

and as far as i can tell its all by the book: http://docs.djangoproject.com/en/dev/ref/templates/builtins/#id5

Alan.

Answer 1

Until Django 1.2 lands you are looking for "Smart If", a Django Template Tag.

A smarter {% if %} tag for django templates.

While retaining current Django functionality, it also handles equality, greater than and less than operators. Some common case examples::

    {% if articles|length >= 5 %}...{% endif %}
    {% if "ifnotequal tag" != "beautiful" %}...{% endif %}

Arguments and operators must have a space between them, so {% if 1>2 %} is not a valid smart if tag.

All supported operators are: or, and, in, = (or ==), !=, >, >=, < and <=.

Answer 2

As mentioned, you can't use operators in the {% if %} tag. It accepts only Boolean values (which you can AND, OR and NOT together.)

For simple equality, you can use the {% ifequal val1 val2 %} tag.

The reason is to push the "logic" out of the template and into the model layer. I.e. you should have a method on your model like so:

def positive_diff(self):
   return self.diff >= 0

Then call that in your template:

{% if x.positive_diff %} ... {% endif %}

Or, you can set an extra variable in your view:

positive_diff = diff >= 0

Answer 3

You need to close each if statement with an endif

{% if var1 %}

{{ var1|safe }} 

{% else %}

{% if var2 %}

{{ var2|safe }}

{% else %}

{% if var3 %}

{{ var3|safe }}

{% endif %}{% endif %}{% endif %}

Answer 4

The "smart if" tag was just added in the development version (that will eventually become 1.2).

If you're using a stable release (1.1.x or earlier) you won't be able to use those comparison operators in the "if" template tag.

Edit: look just above the == operator