Creating Runnable objects with chain decorator

Overview

This tutorial explains how to convert regular functions into Runnable objects using the @chain decorator.

We'll cover ChatPromptTemplate for prompt creation, function transformation with @chain.

The practical exercise demonstrates how to builde a custom chain that converts text into Instagram-style posts with emojis.

Table of Contents

References

Environment Setup

Setting up your environment is the first step. See the Environment Setup guide for more details.

[Note]

  • The langchain-opentutorial is a bundle of easy-to-use environment setup guidance, useful functions and utilities for tutorials.

  • Check out the langchain-opentutorial for more details.

%%capture --no-stderr
%pip install langchain-opentutorial
# Install required packages
from langchain_opentutorial import package

package.install(
    [
        "langchain_core",
        "langchain_openai",
    ],
    verbose=False,
    upgrade=False,
)

You can set API keys in a .env file or set them manually.

[Note] If you’re not using the .env file, no worries! Just enter the keys directly in the cell below, and you’re good to go.

from dotenv import load_dotenv
from langchain_opentutorial import set_env

# Attempt to load environment variables from a .env file; if unsuccessful, set them manually.
if not load_dotenv():
    set_env(
        {
            "OPENAI_API_KEY": "",
            "LANGCHAIN_API_KEY": "",
            "LANGCHAIN_TRACING_V2": "true",
            "LANGCHAIN_ENDPOINT": "https://api.smith.langchain.com",
            "LANGCHAIN_PROJECT": "07-ChainDecorator",
        }
    )

Creating Runnable objects: RunnableLambda vs. chain decorator

As highlighted in LangChain's Conceptual guide, the Runnable interface is a core concept going with many LangChain components. When we use LangChain Expression Language (LCEL) to create a Runnable, we often call it a chain. This means that chains are a specific type of Runnable and therefore inherit all the properties and methods of a Runnable object.

You can create these objects from regular Python functions using two primary methods: RunnableLambda and the @chain decorator.

Let's see how it works in practice!

Define two prompt templates using the ChatPromptTemplate class:

  • prompt1 requests a brief description of a given topic.

  • prompt2 requests the creation of an Instagram post using emojis.

from langchain_core.output_parsers import StrOutputParser
from langchain_core.prompts import ChatPromptTemplate
from langchain_core.runnables import chain
from langchain_openai import ChatOpenAI

# Define prompt templates
prompt1 = ChatPromptTemplate.from_template("Please provide a brief description in English about {topic}.")
prompt2 = ChatPromptTemplate.from_template(
    "Please create an Instagram post using emojis for the following text: {sentence}"
)

Using the RunnableLambda

Let's check the following example, wrapping a regular function instagram_post_generator() with RunnableLambda to create a Runnable object.

from langchain_core.runnables import RunnableLambda

# Using RunnableLambda
def instagram_post_generator(text):
    chain1 = prompt1 | ChatOpenAI(model="gpt-4o-mini") | StrOutputParser()
    output1 = chain1.invoke({"topic": text})
    chain2 = prompt2 | ChatOpenAI(model="gpt-4o-mini") | StrOutputParser()
    return chain2.invoke({"sentence": output1})

runnable_chain = RunnableLambda(instagram_post_generator)
print(runnable_chain.invoke("quantum mechanics"))
🌌✨ Dive into the fascinating world of quantum mechanics! 🔬💫 
    
    🧬 This fundamental branch of physics explores the behavior of matter and energy at the tiniest scales—think atoms and subatomic particles! ⚛️💥
    
    📏 Unlike classical mechanics, quantum mechanics introduces mind-bending concepts like:
    🌊🌀 Wave-particle duality (particles can be both wave-like and particle-like!),
    🔄 Superposition (particles can exist in multiple states at once!),
    🔗 Entanglement (where particles are interconnected across distances! 😲)
    
    🔍 These principles reshape our understanding of reality and fuel groundbreaking technologies such as:
    💻 Quantum computing,
    💡 Lasers,
    🔌 Semiconductors!
    
    Join us on this journey to unravel the mysteries of the quantum realm! 🌟🔭 #QuantumMechanics #Physics #ScienceIsCool #WaveParticleDuality #QuantumComputing #Entanglement #Superposition #Technology #NatureOfReality

Using the chain decorator

You can convert any function into a chain by adding the @chain decorator.

This does the same thing as wrapping the function in RunnableLambda. However, the @chain decorator provides a cleaner and more maintainable way to create Runnable objects in your LangChain applications.

The custom_chain function executes a custom chain based on the input text.

  • By decorating this function with @chain, we convert it into a Runnable object.

@chain
def custom_chain(text):
    # Create a chain by connecting the first prompt, ChatOpenAI, and string output parser
    chain1 = prompt1 | ChatOpenAI(model="gpt-4o-mini") | StrOutputParser()
    output1 = chain1.invoke({"topic": text})

    # Create a chain by connecting the second prompt, ChatOpenAI, and string output parser
    chain2 = prompt2 | ChatOpenAI(model="gpt-4o-mini") | StrOutputParser()
    # Call the second chain with the parsed first result and return the final result
    return chain2.invoke({"sentence": output1})

Since custom_chain is now a Runnable object, it must be executed using invoke().

# Call custom_chain
print(custom_chain.invoke("quantum mechanics"))
🌌✨ Dive into the mysterious world of #QuantumMechanics! 🔬💫 
    
    This fundamental branch of physics reveals how matter and energy behave at the tiniest scales, like atoms and subatomic particles. 🧬⚛️ 
    
    🌀 **Wave-Particle Duality**: Electrons can be both waves and particles! 🌊➡️⚛️ 
    
    🔄 **Superposition**: Systems can exist in multiple states at once! 🎭✨ 
    
    🔗 **Entanglement**: Particles can be connected in a way that the state of one affects the other, no matter the distance! 🌌❤️ 
    
    These mind-blowing concepts are shaping our understanding of the universe and powering technologies like semiconductors, lasers, and quantum computing! 💻🔋 
    
    #Physics #Science #Universe #Technology #Innovation #Quantum #ExploreTheUnknown 🚀🔍🧪
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