Can I perform calculations directly in django tags/filters?

[jago]

I am thinking about something like {{ (width - 5) *12 }} ?

[Rajesh Dhawan]

> I am thinking about something like {{  (width - 5) *12  }}  ?

No. That syntax is not supported in Django templates.

[DavidA]

You can do it in a custom eval-like tag:

@register.tag()
def evalpy(parser, token):
try:
tag_name, expression = token.split_contents()
except ValueError:
raise template.TemplateSyntaxError, "%r tag requires a
single argument" % token.contents.split()[0]
if not (expression[0] == expression[-1] and expression[0] in
('"', "'")):
raise template.TemplateSyntaxError, "%r tag's argument
should be in quotes" % tag_name
return EvalNode(expression[1:-1])

class EvalNode(template.Node):
def __init__(self, expression):
self.expression = expression
def render(self, context):
return eval(self.expression, {}, context)

and then use it like below. Note you can access context/template
variables this way:

{% get_comment_count for post as comment_count %}
<h1>{% evalpy "comment_count + 3" %}</h1>

Kludgy, yes, but sometimes useful.
-Dave

[Daniel Roseman]

On Nov 18, 7:55 pm, jago <java.j...@gmail.com> wrote:
> I am thinking about something like {{  (width - 5) *12  }}  ?

No. You can add or subtract using the 'add' filter:
{{ width:add:"-5" }}
but anything else will require a custom template tag or filter.
Luckily, these are extremely easy to write:

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

{{ width|multiply:12 }}

You'll want to add error checking and so on of course, but that's the
idea.

--
DR.

[Adeotun Adegbaju]

you should indicate which files codes should be added to

[Luqman Shofuleji]

Try using django-mathfilters.

https://pypi.org/project/django-mathfilters/

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