Template Variables | Templates | Langchain Tutorial

Introduction

Template variables are a powerful feature in LangChain that allow you to dynamically substitute values within a template. This can be particularly useful for generating dynamic content, such as personalized messages or data-driven text. In this tutorial, we will explore everything you need to know about template variables, from basic concepts to advanced usage.

Basic Concept

Template variables are placeholders within a string template that get replaced with actual values at runtime. They are typically enclosed in curly braces {}. For example:

Hello, {name}!

In this example, {name} is a template variable that can be replaced with an actual name.

Using Template Variables

To use template variables in LangChain, you typically follow these steps:

Create a template string with placeholders.
Define the actual values for the placeholders.
Render the template with the values.

Here is a simple example:


const template = "Hello, {name}! Welcome to LangChain.";

const values = { name: "John" };

const message = renderTemplate(template, values);

console.log(message); // Output: Hello, John! Welcome to LangChain.

In this example, the renderTemplate function replaces the {name} variable with the value "John".

Advanced Usage

Template variables can also be used in more complex scenarios involving loops, conditionals, and nested templates. Here is an example that demonstrates a loop:


const template = "Items: {#each items}{name}, {/each}";

const values = { items: [{ name: "Item1" }, { name: "Item2" }, { name: "Item3" }] };

const message = renderTemplate(template, values);

console.log(message); // Output: Items: Item1, Item2, Item3,

In this example, the {#each items} block iterates over the items array and replaces {name} with the name of each item.

Best Practices

When using template variables, consider the following best practices:

Keep template strings readable and maintainable.
Avoid deeply nested templates to reduce complexity.
Validate the values to prevent injection attacks.

Conclusion

Template variables in LangChain provide a flexible and powerful way to generate dynamic content. By understanding the basic concepts and advanced usage, you can leverage this feature to create more dynamic and personalized applications. Remember to follow best practices to ensure your templates are maintainable and secure.