PromptTemplate basics in LangChain - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this PromptTemplate render?

Given the PromptTemplate below, what will be the rendered output when input variable 'name' is 'Alice'?

LangChain

from langchain.prompts import PromptTemplate

template = "Hello, {name}! Welcome to LangChain."
prompt = PromptTemplate(template=template, input_variables=["name"])
output = prompt.format(name="Alice")
print(output)

A Hello, Alice! Welcome to {LangChain}.

B Hello, {name}! Welcome to LangChain.

C Hello, name! Welcome to LangChain.

D Hello, Alice! Welcome to LangChain.

💡 Hint

Look at how the variable 'name' is used inside curly braces and how format replaces it.

The PromptTemplate replaces {name} with the value passed in format, which is 'Alice'. So the output is 'Hello, Alice! Welcome to LangChain.'.

📝 Syntax

intermediate

Which option correctly creates a PromptTemplate with two input variables?

You want to create a PromptTemplate with variables 'city' and 'weather'. Which code snippet is correct?

A PromptTemplate(template="The weather in {city} is {weather}.", input_variables="city, weather")

B PromptTemplate(template="The weather in {city} is {weather}.", input_variables=["city", "weather"])

C PromptTemplate(template="The weather in {city} is {weather}.", input_variables={"city", "weather"})

D PromptTemplate(template="The weather in {city} is {weather}.", input_variables=[city, weather])

💡 Hint

input_variables must be a list of strings.

input_variables expects a list of strings naming the variables used in the template. Option B correctly uses a list of strings.

❓ state_output

advanced

What is the output of this PromptTemplate with missing variable?

What happens when you try to format a PromptTemplate but omit one required variable?

LangChain

from langchain.prompts import PromptTemplate

template = "Today in {city}, the temperature is {temp} degrees."
prompt = PromptTemplate(template=template, input_variables=["city", "temp"])
output = prompt.format(city="Paris")
print(output)

A Raises a KeyError because 'temp' is missing

B Outputs: Today in Paris, the temperature is {temp} degrees.

C Outputs: Today in Paris, the temperature is degrees.

D Outputs: Today in {city}, the temperature is {temp} degrees.

💡 Hint

Check what happens if a required variable is not provided to format.

PromptTemplate.format requires all variables listed in input_variables. Omitting 'temp' causes a KeyError.

🧠 Conceptual

advanced

Which statement about PromptTemplate input_variables is true?

Choose the correct statement about the input_variables parameter in PromptTemplate.

A input_variables must list all variables used in the template string exactly.

B input_variables can be omitted if the template uses no variables.

C input_variables can include variables not present in the template string.

D input_variables must be a dictionary mapping variable names to default values.

💡 Hint

Think about how PromptTemplate validates variables.

input_variables must exactly list all variables used in the template. Omitting or adding extra variables causes errors.

🔧 Debug

expert

Why does this PromptTemplate raise a ValueError?

Examine the code and choose the reason for the ValueError.

LangChain

from langchain.prompts import PromptTemplate

template = "Hello, {name}! Your age is {age}."
prompt = PromptTemplate(template=template, input_variables=["name", "age", "location"])
output = prompt.format(name="Bob", age=30, location="NY")
print(output)

A format arguments do not match input_variables types

B format is missing a required variable 'location', causing ValueError

C input_variables includes 'location' which is not in the template, causing ValueError

D template string has syntax error with curly braces

💡 Hint

Check if input_variables matches variables in the template exactly.

PromptTemplate raises ValueError if input_variables list contains variables not present in the template string.