Question: I’m encountering a TemplateSyntaxError in my Django project when rendering a template. The error message I’m seeing is: TemplateSyntaxError at /admin/dashboard/program/add/ Invalid filter: 'length_is' Django Version: 5.1 Python Version: 3.12.4 Error Location: This error appears in a Django template at line 22 of the fieldset.html file. {% for line in fieldset %} <div class="form-group{% if line.fields|length_is:'1' and line.errors %} errors{% endif %}{% if not line.has_visible_field %} hidden{% endif %}{% for field in line %}{% if field.field.name %} field-{{ field.field.name }}{% endif %}{% endfor %}"> <div class="row"> {% for field in line %} <label class="{% if not line.fields|length_is:'1' and forloop.counter != 1 %}col-auto {% else %}col-sm-3 {% endif %}text-left" for="id_{{ field.field.name }}"> {{ field.field.label|capfirst }} {% if field.field.field.required %} <span class="text-red">* </span> {% endif %} </label> <div class="{% if not line.fields|length_is:'1' %} col-auto fieldBox {% else %} col-sm-7 {% endif %} {% if field.field.name %} field-{{ field.field.name }}{% endif %}">  What I Tried: Checked for Custom Filters: I reviewed my project and its installed packages to verify if there is a custom filter named length_is. I found that no such custom filter is defined in my project. Verified Django Installation: I ensured that Django is correctly installed and up-to-date with version 5.1. Reviewed Template Code: I carefully examined the template code that causes the error. I found that line.fields|length_is:'1' is used, but the length_is filter is not a standard Django filter. Searched for Package Bugs: I searched through documentation and bug reports related to django-jazzmin to see if there is any mention of the length_is filter issue, but I could not find relevant information. What I Expected: I expected to find either: Documentation or a reference indicating that length_is is a standard Django filter or a filter provided by an external package. Guidance on how to define or implement the length_is filter if it is a custom filter not included by default. A resolution indicating that the issue might be related to a version mismatch or configuration issue that could be easily resolved. Since I couldn’t find any useful information or documentation about this filter, I’m unsure how to proceed. Any help on defining or correctly using the length_is filter in Django templates would be greatly appreciated.

Answer: Don't copy the old length_is template tag from Django 5.0.x. If this is in an upstream repository, propose the appropriate change to the project (or use the approach provided here: https://github.com/farridav/django-jazzmin/issues/593#issuecomment-2288096357 Update: The specific fix has been merged in: https://github.com/farridav/django-jazzmin/pull/519) This template filter was removed in Django 5.1. The reason for its removal can be found in the Django 5.1 release notes and is explained in the source code:  warnings.warn( "The length_is template filter is deprecated in favor of the length template " "filter and the == operator within an {% if %} tag.", RemovedInDjango51Warning, )  See the source code for more details. Recommended Update Instead of using length_is:'n', update your template to use the length filter with the == operator: Old syntax: {% if value|length_is:'n' %}...{% endif %}  New syntax: {% if value|length == n %}...{% endif %}  You can also handle alternative outputs like this: {% if value|length == n %}True{% else %}False{% endif %}  This approach aligns with Django's recommended practices and ensures your templates are forward-compatible.