Few-shot prompt templates in LangChain - Step-by-Step Execution

Concept Flow - Few-shot prompt templates

Start: Define examples

↓

Create prompt template with examples

↓

Add user input

↓

Generate full prompt

↓

Send prompt to model

↓

Receive model output

↓

Return output to user

This flow shows how few-shot prompt templates combine example pairs with user input to create a prompt for the model, then get and return the output.

Execution Sample

LangChain

from langchain.prompts import PromptTemplate, FewShotPromptTemplate

examples = [
  {"input": "Hello", "output": "Hi!"},
  {"input": "Bye", "output": "Goodbye!"}
]

example_template = PromptTemplate(
  input_variables=["input", "output"],
  template="Input: {input}\nOutput: {output}\n"
)

prompt = FewShotPromptTemplate(
  examples=examples,
  input_variables=["input"],
  example_prompt=example_template,
  suffix="Input: {input}\nOutput: "
)

full_prompt = prompt.format(input="Thanks")

This code creates a few-shot prompt with two examples and formats it with a new input.

Execution Table

Step	Action	Input	Prompt Content	Output
1	Define examples	[{"input": "Hello", "output": "Hi!"}, {"input": "Bye", "output": "Goodbye!"}]	N/A	Examples stored
2	Create FewShotPromptTemplate	examples + input_variables + example_prompt	Template ready with placeholders	Template object created
3	Format prompt with input	"Thanks"	Includes examples + 'Thanks' input	Full prompt string generated
4	Send prompt to model	Full prompt string	Prompt sent to language model	Model processes prompt
5	Receive model output	Model response	N/A	"You're welcome!" (example output)
6	Return output	Model output	N/A	"You're welcome!" returned to user

💡 Process ends after model output is returned to the user.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 5	Final
examples	empty	[{"input": "Hello", "output": "Hi!"}, {"input": "Bye", "output": "Goodbye!"}]	[same]	[same]	[same]	[same]
prompt	undefined	undefined	FewShotPromptTemplate object	FewShotPromptTemplate object	FewShotPromptTemplate object	FewShotPromptTemplate object
full_prompt	undefined	undefined	undefined	Full prompt string with examples and input	Full prompt string	Full prompt string
model_output	undefined	undefined	undefined	undefined	"You're welcome!"	"You're welcome!"

Key Moments - 3 Insights

Why do we include examples in the prompt before the user input?

Including examples shows the model how to respond, guiding it to produce similar answers. See execution_table step 3 where examples are combined with input.

What happens if we forget to format the prompt with the user input?

The prompt will only have examples but no new input, so the model won't know what to answer. Refer to execution_table step 3 where formatting adds the input.

Is the model output always the same for the same input?

No, the model can produce different outputs due to randomness or settings. The example output in step 5 is just one possible answer.

Visual Quiz - 3 Questions

Look at the execution_table at step 3. What does the 'full_prompt' contain?

A Only the examples without user input

B Only the new user input without examples

C Examples plus the new user input formatted together

D An empty string

💡 Hint

Check the 'Prompt Content' column at step 3 in the execution_table.

At which step does the model generate a response?

A Step 5

B Step 2

C Step 4

D Step 6

💡 Hint

Look at the 'Output' column in the execution_table for when the model output appears.

If we add more examples, how does the 'full_prompt' change at step 3?

A It stays the same size

B It includes more example pairs before the user input

C It removes the user input

D It becomes empty

💡 Hint

Refer to how examples are combined with input in the 'Prompt Content' at step 3.

Concept Snapshot

Few-shot prompt templates combine example input-output pairs with new user input.
They create a prompt showing examples first, then the new input.
This guides the model to respond similarly.
Use format() to insert user input into the template.
Send the full prompt to the model to get output.
Useful for teaching the model by example.

Full Transcript

Few-shot prompt templates work by first defining example input-output pairs. Then, these examples are combined with the user's new input to create a full prompt. This prompt is sent to the language model, which generates a response based on the examples and input. The process involves creating the template, formatting it with input, sending it to the model, and returning the output. This method helps the model understand how to respond by showing examples first.