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.