Filters in Jinja templates

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Introduction

Jinja templates are a powerful way to create dynamic prompts. You can use Jinja templates to create prompts that are tailored to the user’s input.

In this guide, we will show you how to use filters in Jinja. You can also learn how to use filters in the prompt editor.

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Filters

In Jinja, filters are functions that modify variables in templates. They work similarly to functions in Python but are used within Jinja templates to transform output dynamically. Filters are applied using a pipe | symbol.

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Basic Syntax

{{ variable | filter_name }}

You can also chain multiple filters:

{{ variable | filter_name1 | filter_name2 }}

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Common Jinja Filters

Here are some frequently used filters:

1. String Filters

• lower: Converts a string to lowercase.

{{ "HELLO" | lower }}  →  hello

• upper: Converts a string to uppercase.

{{ "hello" | upper }}  →  HELLO

• title: Capitalizes the first letter of each word.

{{ "hello world" | title }}  →  Hello World

• capitalize: Capitalizes the first letter of the string.

{{ "hello" | capitalize }}  →  Hello

• reverse: Reverses the string.

{{ "hello" | reverse }}  →  olleh

2. List & Collection Filters

• length: Returns the number of items in a list or string.

{{ ["apple", "banana", "cherry"] | length }}  →  3

• join: Joins a list of strings into a single string.

{{ ["apple", "banana", "cherry"] | join(", ") }}  →  apple, banana, cherry

• first: Returns the first item in a list.

{{ ["apple", "banana", "cherry"] | first }}  →  apple

• sort: Returns the last item in a list.

{{ ["apple", "banana", "cherry"] | sort }}  →  ["apple", "banana", "cherry"]

3. Number Filters

• round: Rounds a number to a specified number of decimal places.

{{ 3.14159 | round(2) }}  →  3.14

• abs: Returns the absolute value of a number.

{{ -5 | abs }}  →  5

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Custom Filters

You can also create your own filters. You can define custom filters in Python and use them in Jinja:

def reverse_string(value):
    return value[::-1]

{{ "hello" | reverse_string }}  →  olleh

Then you can use it in Jinja:

{{ "hello" | reverse_string }}  →  olleh