Modern Flask, Quart, and many lightweight Python backends rely on Jinja2 for templating. But a lot of developers come in with a Django mindset—and sometimes that mindset breaks their templates in very loud, very unhelpful ways.

Let’s walk through two common failure cases, why they happen, and how to fix them in a Jinja2 environment.

1. Passing variables into included templates

Imagine this situation: you have a reusable editor component and want to include it while passing context, such as the content type and field name. You might write something like this:

{% include 'components/editor.html' with content_type='article' field_name='body' %}

This is perfectly valid in Django’s templating engine. Django lets you call include and attach additional variables using with ....

Now look at what happens in a Jinja2 environment.

Jinja2 will raise an error similar to:

TemplateSyntaxError: expected token 'end of statement block', got 'with'

In plain terms, Jinja2 looks at the with keyword inside the include statement and has no idea what you’re trying to do. In Jinja2, include is not a function call that accepts keyword arguments. It’s more like a literal “paste this other file here with the current context.”

How Jinja2 wants you to do it

In Jinja2, there are two common patterns.

Pattern A: Set variables first, then include

You define the variables you want, then you include the component, and that component reads from the current context:

{% set content_type = 'article' %}

{% set field_name = 'body' %}

{% include 'components/editor.html' %}

Inside components/editor.html, you can now safely reference content_type and field_name.

The mental model is: “prepare context in advance, then include.”

Pattern B: Stop using `include` and use macros for components

Once you find yourself trying to “call” a template with different arguments in different places, you’re no longer including a fragment – you’re calling a component. Jinja2’s answer to that problem is a macro.

Example component file:

{# components/editor.html #}

{% macro editor(content_type, field_name) %}

</div>

{% endmacro %}

Then in the template where you need it:

{% from 'components/editor.html' import editor %}

{{ editor('article', 'body') }}

Here, editor(...) behaves like a function call. This is usually the cleaner long-term approach for reusable UI elements such as editors, input groups, tag pickers, alert banners, etc.

The underlying lesson

Django lets you treat include almost like a function that accepts keyword arguments.

Jinja2 does not.

Jinja2 wants either:

“set variables in scope, then include,” or
“define a macro and call it.”

Trying to write Django-style include ... with ... is one of the first places people get burned.

2. Filter syntax and the mysterious colon

Here’s another classic collision. Suppose you want a fallback value for a variable that might not be defined. In Django you may be used to writing:

In Django’s template language, the default filter takes its argument after a colon. So default:'blog' means “if content_type is undefined or empty, use the string 'blog'.”

Now, take that same line and drop it into a Jinja2 template.

Jinja2 responds with something like:

TemplateSyntaxError: expected token 'end of print statement', got ':'

That error tends to confuse people because nothing looks obviously wrong at first glance. But from Jinja2’s perspective, the colon is illegal in that position. The filter argument syntax is different.

How Jinja2 wants you to write it

The equivalent expression in Jinja2 is:

Jinja2 passes filter arguments using parentheses, not with a colon. In other words:

Django: |filter_name:arg
Jinja2: |filter_name(arg)

So default:'blog' in Django becomes default('blog') in Jinja2.

This isn’t just about default. Any filter that takes a parameter follows the same form in Jinja2.

NOTE: Even AIs make these mistakes.

Those two alone cause a surprising amount of pain. Once you correct them, most of the rest of the syntax feels comfortably familiar.