Comparing prompt versions in LangChain

Introduction

Comparing prompt versions helps you see how changes affect the output. It lets you pick the best prompt for your task.

You want to improve chatbot answers by testing different prompts.

You need to check which prompt version gives clearer or more accurate results.

You want to compare how small wording changes affect AI responses.

You are developing a new feature and want to find the best prompt style.

You want to track prompt changes over time to keep improving your app.

Syntax

LangChain

from langchain.prompts import PromptTemplate

# Define two prompt versions
prompt_v1 = PromptTemplate(input_variables=["name"], template="Hello, {name}!")
prompt_v2 = PromptTemplate(input_variables=["name"], template="Hi there, {name}! How can I help?")

# Use prompts with input
output_v1 = prompt_v1.format(name="Alice")
output_v2 = prompt_v2.format(name="Alice")

# Compare outputs
print("Version 1:", output_v1)
print("Version 2:", output_v2)

PromptTemplate is used to create prompt versions with variables.

Use the format method to fill in variables and get the prompt text.

Examples

Simple prompt with one variable for city name.

LangChain

prompt_v1 = PromptTemplate(input_variables=["city"], template="Weather in {city} today is sunny.")
print(prompt_v1.format(city="Paris"))

Prompt with two variables to customize message.

LangChain

prompt_v2 = PromptTemplate(input_variables=["city", "temp"], template="The temperature in {city} is {temp} degrees.")
print(prompt_v2.format(city="London", temp=20))

Another version with a friendlier greeting.

LangChain

prompt_v3 = PromptTemplate(input_variables=["name"], template="Good morning, {name}! Ready for your tasks?")
print(prompt_v3.format(name="Bob"))

Sample Program

This program shows two prompt versions with the same input name. It prints both outputs so you can compare how the prompt wording changes the message.

LangChain

from langchain.prompts import PromptTemplate

# Define two prompt versions
prompt_v1 = PromptTemplate(input_variables=["user"], template="Hello, {user}!")
prompt_v2 = PromptTemplate(input_variables=["user"], template="Hi {user}, how can I assist you today?")

# Format prompts with the same input
output_v1 = prompt_v1.format(user="Emma")
output_v2 = prompt_v2.format(user="Emma")

# Print both outputs to compare
print("Prompt Version 1 Output:", output_v1)
print("Prompt Version 2 Output:", output_v2)

Important Notes

Always keep input variables consistent when comparing prompt versions.

Small wording changes can greatly affect AI responses.

Test prompts with real inputs to see practical differences.

Summary

Comparing prompt versions helps find the best wording for your AI tasks.

Use PromptTemplate and format inputs to generate prompt texts.

Print and review outputs side-by-side to decide which prompt works better.

Practice

1. What is the main purpose of comparing different prompt versions in Langchain?

easy

A. To find the best wording that improves AI task results

B. To increase the number of API calls

C. To reduce the size of the prompt template

D. To change the programming language used

Solution

1. Step 1: Understand the goal of prompt comparison

   Comparing prompt versions helps identify which wording or structure yields better AI responses.

2. Step 2: Eliminate unrelated options

   Increasing API calls, reducing prompt size, or changing language do not relate to improving prompt effectiveness.

3. Final Answer:

   To find the best wording that improves AI task results -> Option A

4. Quick Check:

   Comparing prompts = find best wording [OK]

Hint: Focus on improving AI output quality, not technical details [OK]

Common Mistakes:

• Thinking prompt comparison reduces API calls
• Confusing prompt size with prompt quality
• Assuming language change is the goal

2. Which of the following is the correct way to create a PromptTemplate in Langchain?

easy

A. PromptTemplate(prompt="Hello {name}", args=["name"])

B. PromptTemplate(name="Hello {name}", variables=["name"])

C. PromptTemplate(text="Hello {name}", inputs=["name"])

D. PromptTemplate(template="Hello {name}", input_variables=["name"])

Solution

1. Step 1: Recall PromptTemplate syntax

   The correct constructor uses 'template' for the prompt text and 'input_variables' for placeholders.

2. Step 2: Check each option

   Only PromptTemplate(template="Hello {name}", input_variables=["name"]) uses 'template' and 'input_variables' correctly; others use wrong parameter names.

3. Final Answer:

   PromptTemplate(template="Hello {name}", input_variables=["name"]) -> Option D

4. Quick Check:

   Correct parameters = template + input_variables [OK]

Hint: Remember: 'template' and 'input_variables' are required keys [OK]

Common Mistakes:

• Using 'name' instead of 'template' for prompt text
• Using 'variables' instead of 'input_variables'
• Confusing parameter names

3. Given the code below, what will be printed?

from langchain import PromptTemplate

prompt_v1 = PromptTemplate(template="Hello, {name}!", input_variables=["name"])
prompt_v2 = PromptTemplate(template="Hi {name}, how are you?", input_variables=["name"])

print(prompt_v1.format(name="Alice"))
print(prompt_v2.format(name="Alice"))

medium

A. Hello Alice!
Hi Alice, how are you?

B. Hello, Alice!
Hi Alice, how are you?

C. Hello, {name}!
Hi {name}, how are you?

D. Error: Missing input variable

Solution

1. Step 1: Understand PromptTemplate.format()

   The format method replaces placeholders with provided values, here 'name' is 'Alice'.

2. Step 2: Apply formatting to each prompt

   prompt_v1 becomes "Hello, Alice!" and prompt_v2 becomes "Hi Alice, how are you?".

3. Final Answer:

   Hello, Alice! Hi Alice, how are you? -> Option B

4. Quick Check:

   Formatted prompts show replaced names [OK]

Hint: Format replaces {name} with 'Alice' exactly [OK]

Common Mistakes:

• Ignoring commas or punctuation in output
• Printing raw template without formatting
• Assuming error without missing inputs

4. What is the error in the following code snippet?

from langchain import PromptTemplate

prompt = PromptTemplate(template="Hello, {user}!")
print(prompt.format(name="Bob"))

medium

A. Missing input_variables parameter in PromptTemplate

B. PromptTemplate cannot be imported from langchain

C. Using 'name' instead of 'user' in format call

D. No error, code runs fine

Solution

1. Step 1: Check PromptTemplate parameters

   While 'input_variables' is recommended, it is optional if placeholders are in template.

2. Step 2: Check format call variables

   The template expects 'user' but format is called with 'name', causing a KeyError.

3. Final Answer:

   Using 'name' instead of 'user' in format call -> Option C

4. Quick Check:

   Format keys must match template placeholders [OK]

Hint: Match format keys exactly to template placeholders [OK]

Common Mistakes:

• Assuming missing input_variables causes error
• Thinking import is wrong
• Ignoring variable name mismatch

5. You want to compare two prompt versions to see which generates a more polite greeting. You have these prompts:

prompt_v1 = PromptTemplate(template="Hey {name}, what's up?", input_variables=["name"])
prompt_v2 = PromptTemplate(template="Good day, {name}. How do you do?", input_variables=["name"])

Which approach best helps you compare their effectiveness?

hard

A. Format both prompts with the same name and print outputs side-by-side for review

B. Use only prompt_v1 since it is shorter and simpler

C. Change the input variable names to different ones for each prompt

D. Run prompt_v2 without formatting to see the raw template

Solution

1. Step 1: Understand comparison goal

   You want to see which prompt wording sounds more polite for the same input.

2. Step 2: Use consistent input and print both outputs

   Formatting both prompts with the same name and printing outputs side-by-side lets you compare wording clearly.

3. Final Answer:

   Format both prompts with the same name and print outputs side-by-side for review -> Option A

4. Quick Check:

   Compare outputs side-by-side for best prompt [OK]

Hint: Print both formatted prompts together to compare easily [OK]

Common Mistakes:

• Choosing only one prompt without comparison
• Changing input variable names inconsistently
• Not formatting prompts before comparing