Conditional routing in graphs in LangChain - Mini Project: Build & Apply

Conditional Routing in Graphs with LangChain

📖 Scenario: You are building a simple chatbot flow using LangChain. The chatbot should decide which response path to take based on user input conditions. This is like choosing different roads on a map depending on traffic or weather.

🎯 Goal: Create a LangChain graph with nodes and edges that route conditionally based on user input. The chatbot will ask a question and follow different paths depending on the answer.

📋 What You'll Learn

Create a LangChain graph with at least three nodes

Add a condition variable to decide routing

Use conditional routing to choose the next node based on the condition

Complete the graph with a final node that ends the conversation

💡 Why This Matters

🌍 Real World

Conditional routing in graphs is useful for building chatbots, decision trees, and workflows that change behavior based on user input or data.

💼 Career

Understanding conditional routing in LangChain graphs helps developers create smarter conversational AI and automated systems that adapt to different scenarios.

1

Create initial LangChain graph nodes

Create three LangChain nodes named start_node, yes_node, and no_node. Each node should have a simple prompt string: "Do you like coffee?", "Great! Coffee is awesome.", and "No worries! Tea is nice too.", respectively.

LangChain

# Create three LangChain nodes with the exact names and prompts
# Your code here

Need a hint?

Use Node from langchain.graphs and BasePromptTemplate from langchain.prompts to create nodes with prompts.

2

Add a condition variable for routing

Create a variable called likes_coffee and set it to True. This variable will control which path the graph takes.

LangChain

from langchain.prompts import BasePromptTemplate
from langchain.graphs import Graph, Node

start_node = Node(prompt=BasePromptTemplate(template="Do you like coffee?"))
yes_node = Node(prompt=BasePromptTemplate(template="Great! Coffee is awesome."))
no_node = Node(prompt=BasePromptTemplate(template="No worries! Tea is nice too."))

# Create a boolean variable likes_coffee and set it to True
# Your code here

Need a hint?

Just create a variable named likes_coffee and assign True to it.

3

Add conditional routing edges to the graph

Create a LangChain Graph named chat_graph with start_node as the root. Add edges from start_node to yes_node and no_node using conditions: route to yes_node if likes_coffee is True, else route to no_node.

LangChain

from langchain.prompts import BasePromptTemplate
from langchain.graphs import Graph, Node

start_node = Node(prompt=BasePromptTemplate(template="Do you like coffee?"))
yes_node = Node(prompt=BasePromptTemplate(template="Great! Coffee is awesome."))
no_node = Node(prompt=BasePromptTemplate(template="No worries! Tea is nice too."))

likes_coffee = True

# Create a Graph named chat_graph with start_node as root
# Add conditional edges from start_node to yes_node and no_node based on likes_coffee
# Your code here

Need a hint?

Use Graph(root=start_node) to create the graph. Use add_edge with a condition lambda that returns likes_coffee or its negation.

4

Add a final node to complete the graph

Create a LangChain node named end_node with the prompt "Thanks for chatting!". Add edges from both yes_node and no_node to end_node without conditions to complete the graph.

LangChain

from langchain.prompts import BasePromptTemplate
from langchain.graphs import Graph, Node

start_node = Node(prompt=BasePromptTemplate(template="Do you like coffee?"))
yes_node = Node(prompt=BasePromptTemplate(template="Great! Coffee is awesome."))
no_node = Node(prompt=BasePromptTemplate(template="No worries! Tea is nice too."))

likes_coffee = True

chat_graph = Graph(root=start_node)
chat_graph.add_edge(start_node, yes_node, condition=lambda: likes_coffee)
chat_graph.add_edge(start_node, no_node, condition=lambda: not likes_coffee)

# Create end_node with prompt "Thanks for chatting!"
# Add edges from yes_node and no_node to end_node without conditions
# Your code here

Need a hint?

Create end_node like the other nodes. Add edges from yes_node and no_node to end_node without conditions.