Error handling in chains in LangChain - Mini Project: Build & Apply

Error handling in chains

📖 Scenario: You are building a small LangChain application that processes user input through a chain of steps. Sometimes, errors can happen in these steps. You want to handle errors gracefully so the chain does not crash and can provide a helpful message.

🎯 Goal: Build a LangChain chain with two simple steps and add error handling to catch exceptions during the chain execution.

📋 What You'll Learn

Create a LangChain chain with two steps

Add a configuration variable to control error handling

Use try-except blocks to catch errors in the chain steps

Return a friendly error message if an exception occurs

💡 Why This Matters

🌍 Real World

In real applications, chains of processing steps often need error handling to avoid crashes and provide user-friendly messages.

💼 Career

Understanding error handling in chains is important for building robust applications using LangChain or similar frameworks.

1

Create the initial LangChain chain steps

Create two simple functions called step_one and step_two. step_one should take a string input_text and return it uppercased. step_two should take a string text and return the reversed string.

LangChain

# Define step_one function
# Define step_two function

Need a hint?

Define two functions with the exact names step_one and step_two. Use string methods upper() and slicing [::-1].

2

Add a configuration variable for error handling

Create a boolean variable called enable_error_handling and set it to True. This will control whether error handling is active in the chain.

LangChain

def step_one(input_text: str) -> str:
    return input_text.upper()

def step_two(text: str) -> str:
    return text[::-1]

# Create enable_error_handling variable
# Your code here

Need a hint?

Just create a variable named enable_error_handling and assign it the value True.

3

Add error handling to the chain execution

Create a function called run_chain that takes a string input_text. Inside, if enable_error_handling is True, use a try-except block to call step_one and step_two in sequence and return the final result. If an exception occurs, return the string 'Error occurred in chain'. If enable_error_handling is False, just call the steps without error handling and return the result.

LangChain

def step_one(input_text: str) -> str:
    return input_text.upper()

def step_two(text: str) -> str:
    return text[::-1]

enable_error_handling = True

# Define run_chain function with error handling
# Your code here

Need a hint?

Use try-except inside the if enable_error_handling block to catch any exceptions from calling step_one and step_two.

4

Complete the chain by calling it with sample input

Add a line that calls run_chain with the string 'hello' and assigns the result to a variable called final_output.

LangChain

def step_one(input_text: str) -> str:
    return input_text.upper()

def step_two(text: str) -> str:
    return text[::-1]

enable_error_handling = True

def run_chain(input_text: str) -> str:
    if enable_error_handling:
        try:
            result_one = step_one(input_text)
            result_two = step_two(result_one)
            return result_two
        except Exception:
            return 'Error occurred in chain'
    else:
        result_one = step_one(input_text)
        result_two = step_two(result_one)
        return result_two

# Call run_chain with 'hello' and assign to final_output
# Your code here

Need a hint?

Call run_chain with the exact string 'hello' and assign the result to final_output.