Prompt composition and chaining in LangChain - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this chained prompt?

Consider a Langchain prompt chain where the first prompt extracts a user's name, and the second prompt generates a greeting using that name. What will be the final output if the input is 'Alice'?

LangChain

from langchain.prompts import PromptTemplate
from langchain.chains import SimpleSequentialChain

name_prompt = PromptTemplate(input_variables=["user_input"], template="Extract the name from: {user_input}")
greet_prompt = PromptTemplate(input_variables=["name"], template="Say hello to {name}!")

class NameExtractor:
    def run(self, user_input):
        # Simulate extraction by returning the input directly
        return user_input

class Greeter:
    def run(self, name):
        return f"Hello, {name}!"

extractor = NameExtractor()
greeter = Greeter()

# Simulate chaining
name = extractor.run("Alice")
output = greeter.run(name)
print(output)

A Hello, Alice!

B Hello, user_input!

C Say hello to Alice!

D Extract the name from: Alice

💡 Hint

Think about how the output of the first prompt is used as input for the second.

The first prompt extracts the name 'Alice' which is passed to the second prompt that generates the greeting 'Hello, Alice!'.

📝 Syntax

intermediate

Identify the syntax error in this prompt chain setup

Which option contains the syntax error when defining a Langchain prompt template with multiple input variables?

LangChain

from langchain.prompts import PromptTemplate

# Intended to have two input variables: 'name' and 'age'

# Option A
prompt_a = PromptTemplate(input_variables=["name", "age"], template="Name: {name}, Age: {age}")

# Option B
prompt_b = PromptTemplate(input_variables=["name", "age"], template="Name: {name}, Age: {age}")

# Option C
prompt_c = PromptTemplate(input_variables=["name", "age"], template="Name: {name}, Age: {age}")

# Option D
prompt_d = PromptTemplate(input_variables=["name", "age"], template="Name: {name}, Age: {age}")

A No syntax error

B rorre xatnys oN

C Syntax error due to missing closing brace in template

D o syntax error

💡 Hint

Check the template string for balanced braces.

Option C has a missing closing brace '}' in the template string causing a syntax error.

❓ state_output

advanced

What is the final output after chaining these prompts with state passing?

Given two prompt templates chained where the first extracts a city from input text and the second generates a weather report for that city, what is the output if the input is 'Weather in Paris'?

LangChain

from langchain.prompts import PromptTemplate

extract_city = PromptTemplate(input_variables=["text"], template="Extract city from: {text}")
weather_report = PromptTemplate(input_variables=["city"], template="The weather in {city} is sunny.")

class CityExtractor:
    def run(self, text):
        # Extract city by splitting
        return text.split()[-1]

class WeatherReporter:
    def run(self, city):
        return f"The weather in {city} is sunny."

extractor = CityExtractor()
reporter = WeatherReporter()

city = extractor.run("Weather in Paris")
result = reporter.run(city)
print(result)

A The weather in Paris

B Extract city from: Weather in Paris

C The weather in text is sunny.

D The weather in Paris is sunny.

💡 Hint

Look at how the city is extracted and passed to the weather report prompt.

The city 'Paris' is extracted and used in the second prompt to produce the full weather report.

🔧 Debug

advanced

Why does this chained prompt raise a KeyError?

This Langchain prompt chain raises a KeyError when running. What is the cause?

LangChain

from langchain.prompts import PromptTemplate

prompt1 = PromptTemplate(input_variables=["input_text"], template="Extract keyword from: {input_text}")
prompt2 = PromptTemplate(input_variables=["keyword"], template="Define {keyword}.")

class Chain:
    def run(self, text):
        # Incorrectly passing variable name
        extracted = prompt1.format(input_text=text)
        # Here, 'extracted' is a string, but prompt2 expects 'keyword'
        return prompt2.format(keyword=extracted)

chain = Chain()
output = chain.run("Explain recursion")
print(output)

A TypeError because extracted is not a dict

B KeyError because prompt2 expects 'keyword' but got 'input_text'

C No error, outputs 'Define Explain recursion.'

D SyntaxError due to missing colon

💡 Hint

Check the variable names used in prompt2.format() call.

prompt2 expects a variable named 'keyword' but the code passes 'input_text', causing a KeyError.

🧠 Conceptual

expert

Which option best describes prompt chaining in Langchain?

Select the most accurate description of prompt chaining in Langchain.

A Prompt chaining connects multiple prompts so the output of one becomes the input of the next, enabling complex workflows.

B Prompt chaining runs multiple prompts independently and combines their outputs without passing data between them.

C Prompt chaining is a method to run a single prompt multiple times with different inputs simultaneously.

D Prompt chaining automatically corrects syntax errors in prompt templates during runtime.

💡 Hint

Think about how data flows between prompts in a chain.

Prompt chaining in Langchain means linking prompts so each uses the previous output as input, creating a sequence.