RunnablePassthrough and RunnableLambda in LangChain - Mini Project: Build & Apply

Using RunnablePassthrough and RunnableLambda in Langchain

📖 Scenario: You are building a simple text processing pipeline using Langchain. You want to pass data through unchanged in one step, and then transform it with a custom function in the next step.

🎯 Goal: Create a Langchain pipeline that first uses RunnablePassthrough to pass input text unchanged, then uses RunnableLambda to convert the text to uppercase.

📋 What You'll Learn

Import RunnablePassthrough and RunnableLambda from langchain_core.runnables

Create a RunnablePassthrough instance named passthrough

Create a RunnableLambda instance named to_upper that converts input text to uppercase

Call invoke on passthrough with the string 'hello world'

Call invoke on to_upper with the output from passthrough

💡 Why This Matters

🌍 Real World

RunnablePassthrough and RunnableLambda help build flexible data pipelines where some steps pass data unchanged and others apply custom transformations.

💼 Career

Understanding these runnables is useful for building modular, reusable components in Langchain workflows, common in AI and automation jobs.

1

Import RunnablePassthrough and RunnableLambda

Import RunnablePassthrough and RunnableLambda from langchain_core.runnables.

LangChain

# Your code here

Need a hint?

Use a single import statement to import both classes from langchain_core.runnables.

2

Create RunnablePassthrough instance

Create a RunnablePassthrough instance named passthrough.

LangChain

from langchain_core.runnables import RunnablePassthrough, RunnableLambda
# Your code here

Need a hint?

Create the instance by calling RunnablePassthrough() and assign it to passthrough.

3

Create RunnableLambda instance to uppercase text

Create a RunnableLambda instance named to_upper that converts input text to uppercase using a lambda function.

LangChain

from langchain_core.runnables import RunnablePassthrough, RunnableLambda

passthrough = RunnablePassthrough()
# Your code here

Need a hint?

Use RunnableLambda with a lambda that calls upper() on the input string.

4

Invoke passthrough and then to_upper

Call invoke on passthrough with the string 'hello world' and assign the result to passed_text. Then call invoke on to_upper with passed_text and assign the result to upper_text.

LangChain

from langchain_core.runnables import RunnablePassthrough, RunnableLambda

passthrough = RunnablePassthrough()
to_upper = RunnableLambda(lambda x: x.upper())
# Your code here

Need a hint?

Use invoke method on both instances and assign their outputs to variables as instructed.