How to Use For Loop in Jinja2 Templates with Flask

In Flask, you use a for loop in Jinja2 templates by enclosing the loop inside {% for item in list %} ... {% endfor %} tags. This lets you repeat HTML elements for each item in a list passed from your Flask route.

Syntax

The for loop in Jinja2 uses the syntax {% for item in list %} ... {% endfor %}. Here, item is a variable representing the current element, and list is the iterable you want to loop over.

You place the HTML or template code you want repeated inside the loop tags.

jinja2

{% for item in list %}
  {{ item }}
{% endfor %}

Example

This example shows a Flask app passing a list of fruits to a Jinja2 template. The template uses a for loop to display each fruit in an unordered list.

python + jinja2

from flask import Flask, render_template

app = Flask(__name__)

@app.route('/')
def index():
    fruits = ['Apple', 'Banana', 'Cherry']
    return render_template('fruits.html', fruits=fruits)

# fruits.html template content:
#
# <ul>
# {% for fruit in fruits %}
#   <li>{{ fruit }}</li>
# {% endfor %}
# </ul>

Output

<ul>
  <li>Apple</li>
  <li>Banana</li>
  <li>Cherry</li>
</ul>

Common Pitfalls

• Forgetting to close the loop with {% endfor %} causes template errors.
• Using {{ }} instead of {% %} for the loop tags is incorrect; {{ }} is for expressions, not control flow.
• Passing a non-iterable (like None or a single value) to the loop will cause errors or no output.

jinja2

{# Wrong: missing endfor #}
{% for item in items %}
  {{ item }}

{# Correct #}
{% for item in items %}
  {{ item }}
{% endfor %}

Quick Reference

Usage	Description
{% for item in list %} ... {% endfor %}	Loop over each item in a list or iterable
{{ item }}	Display the current item inside the loop
{% if condition %} ... {% endif %}	Use conditions inside loops for filtering or logic
loop.index	Current loop iteration number starting at 1
loop.first	True if this is the first iteration
loop.last	True if this is the last iteration

Key Takeaways

Use {% for item in list %} ... {% endfor %} to loop over lists in Jinja2 templates.

Always close your for loops with {% endfor %} to avoid errors.

Pass iterable data from Flask routes to templates for looping.

Use {{ item }} inside the loop to display each element.

Leverage loop variables like loop.index for extra control inside loops.