Handling parsing failures in LangChain - Mini Project: Build & Apply

Handling Parsing Failures in Langchain

📖 Scenario: You are building a chatbot using Langchain that extracts user information from text inputs. Sometimes the input text is unclear or incomplete, causing parsing to fail. You want to handle these failures gracefully to improve user experience.

🎯 Goal: Build a Langchain parser that tries to extract a user's name and age from text. If parsing fails, it should return a friendly error message instead of crashing.

📋 What You'll Learn

Create a Langchain parser with a schema for name and age

Add a sample input text variable

Use try-except to catch parsing failures

Return a custom error message on failure

💡 Why This Matters

🌍 Real World

Handling parsing failures is important in chatbots and data extraction tools to avoid crashes and provide helpful feedback to users.

💼 Career

Many software roles require robust error handling when working with user input and external libraries like Langchain.

1

Create the parser schema and sample input

Create a Langchain StructuredOutputParser with a schema that expects name as a string and age as an integer. Also create a variable called input_text with the value "My name is Alice and I am 30 years old."

LangChain

# Your code here

Need a hint?

Use StructuredOutputParser.from_schema() with a dictionary schema. Define input_text exactly as given.

2

Add a variable for the parser output format instructions

Create a variable called format_instructions and set it to the value returned by parser.get_format_instructions()

LangChain

from langchain.output_parsers import StructuredOutputParser

schema = {
    "name": "string",
    "age": "integer"
}

parser = StructuredOutputParser.from_schema(schema)

input_text = "My name is Alice and I am 30 years old."

# Create format_instructions variable here
# Your code here

Need a hint?

Call parser.get_format_instructions() and assign it to format_instructions.

3

Parse the input text with error handling

Use a try-except block to parse input_text with parser.parse(input_text). Assign the result to parsed_output. In the except block, assign parsed_output the string "Parsing failed: please provide name and age clearly."

LangChain

from langchain.output_parsers import StructuredOutputParser

schema = {
    "name": "string",
    "age": "integer"
}

parser = StructuredOutputParser.from_schema(schema)

input_text = "My name is Alice and I am 30 years old."

format_instructions = parser.get_format_instructions()

# Parse input_text with try-except and assign to parsed_output
# Your code here

Need a hint?

Use try to parse and except Exception to catch failures. Assign the error message string to parsed_output in the except block.

4

Add a final print statement to show the parsed output or error

Add a line to print the variable parsed_output so you can see the parsing result or error message.

LangChain

from langchain.output_parsers import StructuredOutputParser

schema = {
    "name": "string",
    "age": "integer"
}

parser = StructuredOutputParser.from_schema(schema)

input_text = "My name is Alice and I am 30 years old."

format_instructions = parser.get_format_instructions()

try:
    parsed_output = parser.parse(input_text)
except Exception:
    parsed_output = "Parsing failed: please provide name and age clearly."

# Print parsed_output
# Your code here

Need a hint?

Use print(parsed_output) to display the result or error message.