RunnablePassthrough and RunnableLambda in LangChain - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a RunnablePassthrough that returns the input as output.

LangChain

from langchain_core.runnables import RunnablePassthrough

passthrough = RunnablePassthrough()
result = passthrough.invoke([1])
print(result)

Drag options to blanks, or click blank then click option'

A'Hello World'

B123

CNone

DTrue

Attempts:

3 left

💡 Hint

Common Mistakes

Passing None or a number instead of a string.

Expecting RunnablePassthrough to modify the input.

The RunnablePassthrough returns exactly what it receives. Passing a string like 'Hello World' will print the same string.

2fill in blank

medium

Complete the code to create a RunnableLambda that doubles the input number.

LangChain

from langchain_core.runnables import RunnableLambda

runnable = RunnableLambda(lambda x: x [1] 2)
result = runnable.invoke(5)
print(result)

Drag options to blanks, or click blank then click option'

A+

B-

C*

D//

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' adds instead of doubling.

Using '//' does integer division, not doubling.

The lambda multiplies the input by 2 to double it. Using '*' performs multiplication.

3fill in blank

hard

Fix the error in the RunnableLambda that should return the input string in uppercase.

LangChain

runnable = RunnableLambda(lambda x: x.[1]())
result = runnable.invoke('hello')
print(result)

Drag options to blanks, or click blank then click option'

Alower

Bupper

Ccapitalize

Dtitle

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'lower()' converts to lowercase, not uppercase.

Using 'capitalize()' only changes the first letter.

The 'upper()' method converts a string to uppercase. This fixes the error to produce 'HELLO'.

4fill in blank

hard

Fill both blanks to create a RunnableLambda that returns the length of the input string if it is longer than 3 characters.

LangChain

runnable = RunnableLambda(lambda x: len(x) if len(x) [1] 3 else [2])
print(runnable.invoke('test'))

Drag options to blanks, or click blank then click option'

A>

B0

CNone

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' reverses the condition.

Returning 0 instead of None changes the meaning.

The lambda checks if the input length is greater than 3 and returns its length; otherwise, it returns None.

5fill in blank

hard

Fill all three blanks to create a RunnableLambda that returns a dictionary with the input string as key and its uppercase as value if the string length is at least 4.

LangChain

runnable = RunnableLambda(lambda x: [1] if len(x) [2] 4 else [3])
print(runnable.invoke('code'))

Drag options to blanks, or click blank then click option'

A{x: x.upper()}

B>=

C{}

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' instead of '>=' excludes strings of length 4.

Returning None instead of an empty dictionary changes the output type.

The lambda returns a dictionary with the input and its uppercase if length is 4 or more; otherwise, it returns an empty dictionary.

Practice

1. What does RunnablePassthrough do with the input it receives?

easy

A. Ignores the input and returns a fixed value

B. Transforms the input using a custom function

C. Returns the input exactly as it is without any changes

D. Throws an error if input is not a string

Solution

1. Step 1: Understand RunnablePassthrough behavior

   RunnablePassthrough is designed to return whatever input it receives without modifying it.

2. Step 2: Compare options with behavior

   Only Returns the input exactly as it is without any changes matches this behavior exactly; others describe transformations or errors which RunnablePassthrough does not do.

3. Final Answer:

   Returns the input exactly as it is without any changes -> Option C

4. Quick Check:

   RunnablePassthrough returns input unchanged = A [OK]

Hint: RunnablePassthrough just passes input through unchanged [OK]

Common Mistakes:

• Thinking RunnablePassthrough modifies input
• Confusing RunnablePassthrough with RunnableLambda
• Assuming it throws errors on certain inputs

2. Which of the following is the correct way to create a RunnableLambda that doubles a number input?

easy

A. RunnableLambda(lambda x: x + 2)

B. RunnableLambda(lambda x: x * 2)

C. RunnableLambda(lambda x: x / 2)

D. RunnableLambda(lambda x: x - 2)

Solution

1. Step 1: Identify the doubling function

   Doubling means multiplying the input by 2, so the function should be lambda x: x * 2.

2. Step 2: Match with options

   RunnableLambda(lambda x: x * 2) matches the doubling function exactly; others perform addition, division, or subtraction.

3. Final Answer:

   RunnableLambda(lambda x: x * 2) -> Option B

4. Quick Check:

   Doubling function uses multiplication by 2 = D [OK]

Hint: Doubling means multiply input by 2 in lambda [OK]

Common Mistakes:

• Using addition instead of multiplication
• Confusing division or subtraction for doubling
• Incorrect lambda syntax

3. What will be the output of this code?

passthrough = RunnablePassthrough()
lambda_runner = RunnableLambda(lambda x: x.upper())
result = lambda_runner.invoke(passthrough.invoke('hello'))
print(result)

medium

A. 'HELLO'

B. 'hello'

C. Error: RunnablePassthrough cannot be invoked

D. 'Hello'

Solution

1. Step 1: Trace RunnablePassthrough output

   Calling passthrough.invoke('hello') returns 'hello' unchanged.

2. Step 2: Apply RunnableLambda function

   The lambda converts input to uppercase, so 'hello'.upper() returns 'HELLO'.

3. Final Answer:

   'HELLO' -> Option A

4. Quick Check:

   Passthrough returns input, lambda uppercases it = C [OK]

Hint: Passthrough returns input, lambda transforms it [OK]

Common Mistakes:

• Expecting passthrough to modify input
• Confusing case conversion result
• Assuming runtime error on invoke

4. Identify the error in this code snippet:

lambda_runner = RunnableLambda(lambda x: x + 1)
result = lambda_runner.invoke('5')
print(result)

medium

A. TypeError because string '5' cannot be added to integer 1

B. SyntaxError in lambda function

C. RunnableLambda cannot be invoked with strings

D. No error; output will be '51'

Solution

1. Step 1: Analyze lambda operation on input

   The lambda tries to add 1 to input '5', which is a string, causing a type mismatch.

2. Step 2: Identify error type

   Adding integer 1 to string '5' raises a TypeError in Python.

3. Final Answer:

   TypeError because string '5' cannot be added to integer 1 -> Option A

4. Quick Check:

   Adding int to string causes TypeError = B [OK]

Hint: Adding int to string causes TypeError in Python [OK]

Common Mistakes:

• Assuming implicit string to int conversion
• Thinking output is string concatenation
• Confusing error types

5. You want to create a LangChain workflow that takes a list of numbers, passes it unchanged, then doubles each number. Which combination of RunnablePassthrough and RunnableLambda is correct?

hard

A. Use RunnablePassthrough twice, no lambda needed

B. Use RunnableLambda with lambda x: x, then RunnablePassthrough to double numbers

C. Use RunnableLambda with lambda x: x*2, then RunnablePassthrough to pass list

D. Use RunnablePassthrough to pass the list, then RunnableLambda with lambda x: [i*2 for i in x]

Solution

1. Step 1: Pass list unchanged with RunnablePassthrough

   RunnablePassthrough returns the list as is, so it fits the first step.

2. Step 2: Double each number with RunnableLambda

   RunnableLambda with lambda x: [i*2 for i in x] correctly doubles each element in the list.

3. Final Answer:

   Use RunnablePassthrough to pass the list, then RunnableLambda with lambda x: [i*2 for i in x] -> Option D

4. Quick Check:

   Passthrough passes list, lambda doubles elements = A [OK]

Hint: Passthrough passes input; lambda transforms list elements [OK]

Common Mistakes:

• Trying to double list with passthrough
• Using lambda that multiplies list object, not elements
• Reversing order of passthrough and lambda