Debugging failed chains in LangChain - Mini Project: Build & Apply

Debugging Failed Chains in Langchain

📖 Scenario: You are building a simple Langchain application that chains two steps: one to get a greeting and another to add a farewell. Sometimes the chain fails silently. You want to debug and fix it.

🎯 Goal: Build a Langchain chain with two steps and add debugging to catch and show errors when the chain fails.

📋 What You'll Learn

Create a Langchain chain with two simple steps

Add a configuration variable to enable debugging

Implement the chain execution with error handling

Add final code to print error details if the chain fails

💡 Why This Matters

🌍 Real World

Debugging chains is important when building multi-step language model workflows to find and fix errors quickly.

💼 Career

Understanding how to debug Langchain chains helps developers maintain reliable AI applications and troubleshoot issues efficiently.

1

Create the initial Langchain chain steps

Create two functions called greeting_step and farewell_step. greeting_step returns the string 'Hello'. farewell_step returns the string 'Goodbye'.

LangChain

# Your code here

Need a hint?

Define two simple functions that return fixed strings.

2

Add a debug flag configuration

Create a variable called debug_mode and set it to True to enable debugging.

LangChain

def greeting_step():
    return 'Hello'

def farewell_step():
    return 'Goodbye'

# Your code here

Need a hint?

Just create a variable named debug_mode and set it to True.

3

Run the chain with error handling

Write a function called run_chain that calls greeting_step() and farewell_step(). Combine their results with a space in between. Use a try-except block to catch any exceptions. If debug_mode is True, print the error message inside the except block.

LangChain

def greeting_step():
    return 'Hello'

def farewell_step():
    return 'Goodbye'

debug_mode = True

# Your code here

Need a hint?

Use try-except to catch errors and print them if debugging is on.

4

Add final call to run the chain and handle failure

Call the run_chain() function and store the result in a variable called result. If result is None, print 'Chain failed.'. Otherwise, print result.

LangChain

def greeting_step():
    return 'Hello'

def farewell_step():
    return 'Goodbye'

debug_mode = True

def run_chain():
    try:
        part1 = greeting_step()
        part2 = farewell_step()
        return part1 + ' ' + part2
    except Exception as e:
        if debug_mode:
            print(f'Error in chain: {e}')
        return None

# Your code here

Need a hint?

Call the chain, check if it failed, and print the right message.