Partial prompt templates in LangChain - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this partial prompt template rendering?

Given this Langchain partial prompt template code, what will be the final rendered prompt string?

LangChain

from langchain.prompts import PromptTemplate

partial_template = PromptTemplate(
    input_variables=["name"],
    template="Hello, {name}!"
)

full_template = partial_template.partial()

result = full_template.format(name="Alice")

A "Hello!"

B "Hello, {name}!"

C "Hello, Alice!"

D "{name}!"

💡 Hint

Think about how partial templates fill in variables and then format works.

The partial template here is created from a template with one variable 'name'. Calling partial() without arguments returns a new PromptTemplate that still expects 'name'. Formatting with name='Alice' replaces {name} with 'Alice', so the output is 'Hello, Alice!'.

📝 Syntax

intermediate

Which option correctly creates a partial prompt template with a fixed variable?

You want to fix the variable 'greeting' to 'Hi' in a prompt template and leave 'name' variable open. Which code snippet correctly does this?

LangChain

from langchain.prompts import PromptTemplate

base_template = PromptTemplate(
    input_variables=["greeting", "name"],
    template="{greeting}, {name}!"
)

# Choose the correct partial template creation:

A partial = base_template.partial(name="Hi")

B partial = base_template.partial(greeting="Hi")

C partial = base_template.partial(greeting)

D partial = base_template.partial("Hi")

💡 Hint

partial() takes keyword arguments to fix variables.

partial() requires keyword arguments to fix variables. Option B correctly fixes 'greeting' to 'Hi'. Option B fixes 'name' instead, which is not what we want. Options C and D are invalid syntax.

❓ state_output

advanced

What is the output after formatting a partial prompt with multiple fixed variables?

Consider this code snippet. What is the value of 'final_prompt' after formatting?

LangChain

from langchain.prompts import PromptTemplate

base = PromptTemplate(
    input_variables=["greeting", "name", "time"],
    template="{greeting}, {name}! Good {time}."
)

partial1 = base.partial(greeting="Hello")
partial2 = partial1.partial(time="morning")

final_prompt = partial2.format(name="Bob")

A "Hello, Bob! Good morning."

B "{greeting}, Bob! Good {time}."

C "Hello, {name}! Good morning."

D "Hello, Bob! Good {time}."

💡 Hint

Each partial fixes one variable. Formatting replaces the remaining variable.

First partial fixes 'greeting' to 'Hello'. Second partial fixes 'time' to 'morning'. Only 'name' remains. Formatting with name='Bob' replaces {name} with 'Bob'. So the final prompt is 'Hello, Bob! Good morning.'.

🔧 Debug

advanced

Why does this partial prompt template raise a KeyError?

This code raises a KeyError when formatting. What is the cause?

LangChain

from langchain.prompts import PromptTemplate

base = PromptTemplate(
    input_variables=["greeting", "name"],
    template="{greeting}, {name}!"
)

partial = base.partial(greeting="Hi")

result = partial.format()

A SyntaxError due to missing colon in template

B TypeError because partial() was called without arguments

C ValueError because 'greeting' is fixed twice

D KeyError because 'name' variable is missing in format() call

💡 Hint

Check which variables remain unfixed when calling format().

The partial fixes 'greeting' but 'name' remains required. Calling format() without 'name' causes a KeyError because the template expects {name} but it is not provided.

🧠 Conceptual

expert

How does chaining partial prompt templates affect input variables?

If you chain multiple partial() calls on a PromptTemplate, how does the set of input variables change?

A Each partial() call fixes some variables, reducing the input_variables list accordingly

B Partial() calls add new variables to input_variables

C Input variables remain unchanged until the final format() call

D Each partial() call resets input_variables to the original full list

💡 Hint

Think about how fixing variables affects what remains to be filled.

Each partial() call fixes some variables, so the new PromptTemplate returned has fewer input_variables. This means the list shrinks as variables get fixed.