DEV Community

Cover image for HTML comments in Django: be careful
guzmanojero
guzmanojero

Posted on • Edited on • Originally published at stackoverflow.com

HTML comments in Django: be careful

HTML comments are not ignored by the Django parser.

If there is an error inside the html comment, an error will still be raised.

For example, you have an url tag directed to a non existent URL name:

<!--<a href="{% url 'prova' %}">Prova</a>-->

Even it it's a comment a NoReverseMatch error will be raised:

NoReverseMatch: Reverse for 'prova' not found. 'prova' is not a valid view function or pattern name.
Enter fullscreen mode Exit fullscreen mode

Be careful with HTML Comments with Unclosed Tags.

Go to a Django project and write this line in a template

<!-- {% if context %} -->

What happens is that Django will raise this error:

TemplateSyntaxError: Unclosed tag on line XXX: 'if'. Looking for one of: elif, else, endif.
Enter fullscreen mode Exit fullscreen mode

Wait, what? Why is a comment raising an error? Aren't comments ignored?
Well... yes and no.*


Why is this happening?

  • The Django template engine parses everything, including content inside HTML comments (<!-- ... -->). So html comments aren't ignored (the no part).*

  • When it encounters {% if context %}, even if it's inside an html comment, it expects a matching {% endif %}. Since the endif is missing, an error is raised.

  • Django treats HTML comments <!-- ... --> as text, not as special syntax.

  • HTML comments are meant to be passed to the browser, although they are not displayed. Django processes their content because it doesn’t know you intend them to be ignored. Try it, make an html comment and then check the page source, html comments are there.

And if you close the tag, no error happens.

<!-- {% if context %} {% endif %} -->


What to do if I want to make a comment with an unclosed tag?

Use Django's Template comments and not html's. Django template's comments are ignored and aren't passed to the browser (the yes part).*

You have two options:

  1. Use comment syntax to comment-out part of a line in a template:
{# {% if context %} #}
Enter fullscreen mode Exit fullscreen mode
  1. Use the comment tag for multiline comment, it ignores everything between them.
{% comment %}  {% if context %} {% endcomment %}
Enter fullscreen mode Exit fullscreen mode

Image of AssemblyAI

Automatic Speech Recognition with AssemblyAI

Experience near-human accuracy, low-latency performance, and advanced Speech AI capabilities with AssemblyAI's Speech-to-Text API. Sign up today and get $50 in API credit. No credit card required.

Try the API

Top comments (0)

AWS Security LIVE!

Tune in for AWS Security LIVE!

Join AWS Security LIVE! for expert insights and actionable tips to protect your organization and keep security teams prepared.

Learn More

👋 Kindness is contagious

Explore a sea of insights with this enlightening post, highly esteemed within the nurturing DEV Community. Coders of all stripes are invited to participate and contribute to our shared knowledge.

Expressing gratitude with a simple "thank you" can make a big impact. Leave your thanks in the comments!

On DEV, exchanging ideas smooths our way and strengthens our community bonds. Found this useful? A quick note of thanks to the author can mean a lot.

Okay