How to set a variable from within a template

Question

My layout template contains a header and I'd like to add a CSS class to the currently selected menu option.

class="active"

I thought I found the solution here but I'm still having issues. When I paste the following code into my template I get a server error.

{% rule = request.url_rule %}

Why didn't this work? How can I set a variable to control the menu in the templates?

when you run your flask app, run it with `app.run(debug=True)` you will get the actual traceback that way (along with an interactive shell and some other cool stuff) — Joran Beasley, Apr 27 '15 at 16:50

score 3 · Accepted Answer · answered Apr 27 '15 at 17:40

{% rule = request.url_rule %} is not valid syntax in Jinja. If you want to set a context variable from a template, use set:

{% set rule = request.rule %}

request is already passed to each template context automatically, you don't need to pass it in render_template.

score 1 · Answer 2 · answered Apr 27 '15 at 16:44

1

My best guess would be that the request object isn't getting passed to the template. If it isn't being passed you wouldn't be able to access it when rendering the template. You could pass it explicitly, which would look something like this:

from flask import request
from flask import render_template

@app.route('/hello/')
def hello():
    return render_template('hello.html', request=request)

answered Apr 27 '15 at 16:44

neatnick

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1

or even better just add a context wrapper thing that makes request available to all views – Joran Beasley Apr 27 '15 at 16:52

Philip Kirkbride · Answer 3 · 2015-04-27T17:58:51.997

Someone commented that swankswashbucklers answer wouldn't fix my problem so I'm posting my solution which was inspired by his suggestion.

I simply manually set a variable called title when creating the view.

def home():
return render_template(
    'index.html',
    title='Home',
)

Within the template I referenced the variable to decide which menu item to highlight.

                    {% if title == "Home" %}
                    <li class="active">
                    {% else %}
                    <li>
                    {% endif %}

It turned out in my situation I didn't need to access the current url.

How to set a variable from within a template

3 Answers3