Sequential chains in LangChain - Mini Project: Build & Apply

Building a Sequential Chain with LangChain

📖 Scenario: You are creating a simple text processing pipeline using LangChain. This pipeline will take a user's input, process it through two steps sequentially, and produce a final output.

🎯 Goal: Build a sequential chain in LangChain that first converts input text to uppercase, then appends a friendly message.

📋 What You'll Learn

Create two simple functions that process text

Create a SequentialChain using LangChain

Connect the functions in the chain in the correct order

Run the chain with a sample input

💡 Why This Matters

🌍 Real World

Sequential chains help automate multi-step text processing tasks, like formatting user input before sending it to a chatbot or API.

💼 Career

Understanding how to build and run sequential chains is useful for developers working with AI pipelines, chatbots, and automation workflows.

1

Create two text processing functions

Write two Python functions: to_uppercase that takes a string text and returns it in uppercase, and add_greeting that takes a string text and returns it with the string ' Have a nice day!' appended.

LangChain

# Your code here

Need a hint?

Define two functions exactly named to_uppercase and add_greeting with one parameter text.

2

Import LangChain and prepare chain components

Import SequentialChain from langchain.chains. Then create two SimpleChain objects named chain1 and chain2 that wrap the functions to_uppercase and add_greeting respectively.

LangChain

def to_uppercase(text: str) -> str:
    return text.upper()

def add_greeting(text: str) -> str:
    return text + ' Have a nice day!'

# Your code here

Need a hint?

Import SequentialChain and SimpleChain. Wrap each function in a SimpleChain with correct input and output keys.

3

Create the SequentialChain

Create a SequentialChain named seq_chain that runs chain1 followed by chain2. Set input_variables to ["text"] and output_variables to ["final_text"].

LangChain

from langchain.chains import SequentialChain, SimpleChain

def to_uppercase(text: str) -> str:
    return text.upper()

def add_greeting(text: str) -> str:
    return text + ' Have a nice day!'

chain1 = SimpleChain(func=to_uppercase, input_key="text", output_key="upper_text")
chain2 = SimpleChain(func=add_greeting, input_key="upper_text", output_key="final_text")

# Your code here

Need a hint?

Create seq_chain with the two chains in order and specify input and output variables.

4

Run the SequentialChain with sample input

Call seq_chain.run with the argument text="hello world" and assign the result to a variable named result.

LangChain

from langchain.chains import SequentialChain, SimpleChain

def to_uppercase(text: str) -> str:
    return text.upper()

def add_greeting(text: str) -> str:
    return text + ' Have a nice day!'

chain1 = SimpleChain(func=to_uppercase, input_key="text", output_key="upper_text")
chain2 = SimpleChain(func=add_greeting, input_key="upper_text", output_key="final_text")

seq_chain = SequentialChain(
    chains=[chain1, chain2],
    input_variables=["text"],
    output_variables=["final_text"]
)

# Your code here

Need a hint?

Run the chain with text="hello world" and save the output in result.