Sequential chains in LangChain - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple sequential chain with two steps.

LangChain

from langchain.chains import SequentialChain
from langchain.llms import OpenAI

llm = OpenAI()

chain = SequentialChain(chains=[[1]], input_variables=["input"], output_variables=["output"])

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

ASequentialChain

Bchain1, chain2

Cllm

Dchain1

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the llm object directly instead of a chain.

Passing multiple chains without wrapping them in a list.

Using the class name instead of an instance.

The chains parameter expects a list of chain objects. Here, chain1 is a single chain object, so it should be passed as a list with one element. Since the code shows only one chain, the correct answer is chain1.

2fill in blank

medium

Complete the code to run the sequential chain with the correct input variable.

LangChain

result = chain.run([1]="Hello")

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

Ainput

Boutput

Ctext

Dquery

Attempts:

3 left

💡 Hint

Common Mistakes

Using the output variable as input.

Using a variable name not defined in the chain.

The input variable for the sequential chain is named input, so you must pass the input value with the key input.

3fill in blank

hard

Fix the error in the code by choosing the correct method to add chains to the SequentialChain.

LangChain

from langchain.chains import SequentialChain

chain = SequentialChain()
chain.[1](chain1)

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

Aadd

Badd_chain

Cappend

Dextend

Attempts:

3 left

💡 Hint

Common Mistakes

Using list methods like append or extend which are not defined.

Using a method name that does not exist in the class.

The SequentialChain class uses the add method to add a chain to the sequence.

4fill in blank

hard

Fill both blanks to create a SequentialChain with two chains and specify the correct input and output variables.

LangChain

chain = SequentialChain(chains=[[1], [2]], input_variables=["input"], output_variables=["final_output"])

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

Achain1

Bchain2

Cchain3

Dchain4

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same chain twice.

Using chains not defined in the code.

To create a sequential chain with two chains, you list them inside the chains parameter. Here, chain1 and chain2 are the correct chains to use.

5fill in blank

hard

Fill all three blanks to define a SequentialChain with input, output, and intermediate variables correctly.

LangChain

chain = SequentialChain(
    chains=[[1], [2]],
    input_variables=[[3]],
    output_variables=["result"]
)

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

AchainA

BchainB

C"user_input"

D"input_text"

Attempts:

3 left

💡 Hint

Common Mistakes

Not quoting the input variable name.

Using undefined chain names.

The chains are chainA and chainB. The input variable is named input_text as a string, so it must be passed with quotes.

Practice

1. What is the main purpose of a SequentialChain in Langchain?

easy

A. To create a single chain that never passes outputs

B. To run multiple chains all at the same time independently

C. To run multiple chains one after another, passing outputs as inputs

D. To stop chains from running automatically

Solution

1. Step 1: Understand SequentialChain behavior

   A SequentialChain runs chains in order, passing output from one to the next.

2. Step 2: Compare options to this behavior

   Only To run multiple chains one after another, passing outputs as inputs describes this step-by-step passing of outputs between chains.

3. Final Answer:

   To run multiple chains one after another, passing outputs as inputs -> Option C

4. Quick Check:

   SequentialChain = run chains sequentially with output passing [OK]

Hint: Sequential means one after another with output passing [OK]

Common Mistakes:

• Thinking chains run in parallel
• Believing outputs are not passed
• Confusing SequentialChain with single chain

2. Which of the following is the correct way to create a SequentialChain with two chains named chain1 and chain2?

easy

A. SequentialChain([chain1, chain2])

B. SequentialChain(chains=[chain1, chain2], input_variables=["input"], output_variables=["output"])

C. SequentialChain(chain1, chain2)

D. SequentialChain(chains=chain1 + chain2)

Solution

1. Step 1: Recall SequentialChain constructor

   It requires a list of chains and lists of input and output variable names.

2. Step 2: Check each option's syntax

   Only SequentialChain(chains=[chain1, chain2], input_variables=["input"], output_variables=["output"]) correctly uses named parameters with lists for chains and variables.

3. Final Answer:

   SequentialChain(chains=[chain1, chain2], input_variables=["input"], output_variables=["output"]) -> Option B

4. Quick Check:

   Correct constructor syntax = SequentialChain(chains=[chain1, chain2], input_variables=["input"], output_variables=["output"]) [OK]

Hint: Look for named parameters and list brackets [OK]

Common Mistakes:

• Passing chains without list brackets
• Missing input/output variable lists
• Using plus operator to combine chains

3. Given the following code snippet, what will be the final output printed?

from langchain.chains import SequentialChain

chain1 = SomeChain()  # outputs {'intermediate': 'hello'}
chain2 = SomeChain()  # expects input 'intermediate' and outputs {'final': 'hello world'}

seq_chain = SequentialChain(chains=[chain1, chain2], input_variables=['input'], output_variables=['final'])

result = seq_chain.run({'input': 'start'})
print(result)

medium

A. Error: missing input for chain2

B. 'hello world'

C. 'start'

D. {'final': 'hello world'}

Solution

1. Step 1: Understand chain outputs and inputs

   chain1 outputs {'intermediate': 'hello'}, chain2 uses 'intermediate' input and outputs {'final': 'hello world'}.

2. Step 2: SequentialChain runs chain1 then chain2, passing outputs

   Final result is {'final': 'hello world'}, printed as "{'final': 'hello world'}".

3. Final Answer:

   {'final': 'hello world'} -> Option D

4. Quick Check:

   Output of SequentialChain = {'final': 'hello world'} [OK]

Hint: Final output is dict of output_variables [OK]

Common Mistakes:

• Expecting string instead of dict repr
• Confusing input and output keys
• Assuming error due to input passing

4. What is the error in this code snippet that tries to create a SequentialChain?

seq_chain = SequentialChain(chains=[chain1, chain2], input_variables=['input'])
result = seq_chain.run({'input': 'data'})

medium

A. Missing output_variables parameter causes an error

B. Chains list should be a tuple, not a list

C. Input dictionary keys do not match input_variables

D. run() method requires no arguments

Solution

1. Step 1: Check required parameters for SequentialChain

   Both input_variables and output_variables are required parameters.

2. Step 2: Identify missing parameter

   The code misses output_variables, so it will raise an error.

3. Final Answer:

   Missing output_variables parameter causes an error -> Option A

4. Quick Check:

   output_variables missing = error [OK]

Hint: Always provide input and output variable lists [OK]

Common Mistakes:

• Forgetting output_variables
• Using wrong data type for chains
• Passing arguments incorrectly to run()

5. You want to build a SequentialChain that first extracts keywords from text, then summarizes those keywords. Which approach correctly sets up this workflow?

hard

A. Create two chains: keyword_extractor outputs 'keywords'; summary_chain takes 'keywords' as input; combine with SequentialChain passing these variables

B. Create one chain that does both extraction and summary in one step

C. Run keyword_extractor and summary_chain separately without chaining outputs

D. Use SequentialChain but ignore passing variables between chains

Solution

1. Step 1: Identify the workflow steps

   First extract keywords, then summarize them, so output of first is input of second.

2. Step 2: Use SequentialChain with proper variable passing

   Set keyword_extractor to output 'keywords', summary_chain to input 'keywords', then chain them sequentially.

3. Final Answer:

   Create two chains: keyword_extractor outputs 'keywords'; summary_chain takes 'keywords' as input; combine with SequentialChain passing these variables -> Option A

4. Quick Check:

   SequentialChain passes outputs as inputs [OK]

Hint: Chain outputs must match next chain inputs [OK]

Common Mistakes:

• Trying to do both steps in one chain
• Not passing outputs to next chain
• Ignoring variable names in chaining