nnA powerful feature of Jinja is the ability to **filter a sequence directly within a `for` loop**. Unlike Python, Jinja does not have `break` or `continue` statements to exit or skip iterations. Instead, you can add a conditional expression to the `for` loop itself to include or exclude items. This method allows you to iterate over a subset of your data while keeping your template clean and readable.nn

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How It Works

nThe conditional expression is added at the end of the `for` loop’s declaration using the `if` keyword. The expression is evaluated for each item in the sequence, and only those items for which the condition is `true` will be included in the loop’s iteration. This is a significant advantage because it ensures that special loop variables like `loop.index` and `loop.length` will accurately reflect the items being iterated over, rather than counting the items that were skipped.n

Syntax

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{% for item in sequence if condition %}n    <!-- Code to render for items that meet the condition -->n{% endfor %}

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Demonstration with Code Samples

nHere are some practical examples of how to use conditional filtering to control your loop’s behavior.n

1. Skipping Hidden Users

nThis is a classic use case for conditional filtering, as it allows you to easily display a list of users while hiding those with a specific property.nnJinja2 Templaten

{% set users = [n    {'username': 'Alice', 'hidden': false},n    {'username': 'Bob', 'hidden': true},n    {'username': 'Charlie', 'hidden': false}n] %}n<ul>n{% for user in users if not user.hidden %}n    <li>{{ loop.index }}. {{ user.username|e }}</li>n{% endfor %}n</ul>

nExplanation: The loop is set to only iterate over users where `user.hidden` is not true. This means “Bob” is skipped, and the loop processes “Alice” and “Charlie.” Crucially, the `loop.index` for “Charlie” will be `2`, as the loop correctly only counts the items it renders.nn

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2. Displaying Only In-Stock Products

nThis example demonstrates how to filter a list of products to display only those that are currently in stock, which is useful for an e-commerce website.nnJinja2 Templaten

{% set products = [n    {'name': 'Laptop', 'in_stock': true},n    {'name': 'Mouse', 'in_stock': false},n    {'name': 'Keyboard', 'in_stock': true}n] %}n<table>n    <thead><tr><th>#</th><th>Product Name</th></tr></thead>n    <tbody>n    {% for product in products if product.in_stock %}n    <tr>n        <td>{{ loop.index }}</td>n        <td>{{ product.name|e }}</td>n    </tr>n    {% endfor %}n    </tbody>n</table>

nExplanation: The loop only processes products where `in_stock` is true. The `Mouse` product is skipped, and the table correctly displays the `Laptop` as row 1 and the `Keyboard` as row 2. The `loop.index` variable is automatically correct for the filtered list.nn