multiplication in django template without using manually created template tag

There are 2 approaches:

• Computing the values inside the view and pass them to the template (recommended in my opinion)
• Using template filters

In the manner of the add filter, you could always create your own multiply filter, creating your own custom filter:

from django import template

register = template.Library()

@register.filter
def multiply(value, arg):
    return value * arg

Then in your template, something like that should work.

{{ quantity | multiply:price }}

This is not tested, and I never did this as - again - I find neater to compute datas inside the views and render only with the templates.

Another approach that I have used seems cleaner to me. If you are going through a queryset, it doesn't make sense to compute the values in your view. Instead, add the calculation as a function in your model!

Let's say your model looks like this:

Class LineItem:
    product = models.ForeignKey(Product)
    quantity = models.IntegerField()
    price = models.DecimalField(decimal_places=2)

Simply add the following to the model:

    def line_total(self):
        return self.quantity * self.price

Now you can simply treat line_total as if it were a field in the record:

{{ line_item.line_total }}

This allows the line_total value to be used anywhere, either in templates or views, and ensures that it is always consistent, without taking up space in the database.

You can use the built-in widthratio template tag.

• a*b use {% widthratio a 1 b %}
• a/b use {% widthratio a b 1 %}

Note: the results are rounded to an integer before returning.

@see https://docs.djangoproject.com/en/dev/ref/templates/builtins/