Partial prompt templates in LangChain - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a partial prompt template in Langchain?

A partial prompt template is a reusable prompt piece where some variables are fixed, and others remain open to be filled later. It helps build complex prompts step-by-step.

beginner

How do partial prompt templates improve prompt building?

They let you fix some parts of a prompt early and fill in the rest later, making prompt creation modular, easier to manage, and reusable.

intermediate

What Langchain method is used to create partial prompt templates?

PromptTemplate's .partial() method. It allows you to set some variables upfront and leave others to be provided later.

intermediate

What happens if you try to format a partial prompt template without providing all remaining variables?

It will raise an error because all variables not fixed in the partial template must be provided when formatting the final prompt.

beginner

Give a simple example of creating and using a partial prompt template in Langchain.

Example: Create a partial prompt fixing 'language' variable:
partial = PromptTemplate.from_template('Translate to {language}: {text}').partial(language='French')
Then format with text:
partial.format(text='Hello') outputs 'Translate to French: Hello'.

What is the main benefit of using partial prompt templates?

A Reuse parts of prompts by fixing some variables early

B Automatically generate prompts without variables

C Replace all variables at once

D Avoid using variables in prompts

Partial prompt templates let you fix some variables early and reuse that part, making prompt building modular.

Which method creates a partial prompt template from a full template string?

A PromptTemplate.create_partial()

B PromptTemplate.from_template().partial()

C PartialPromptTemplate.new()

D PromptTemplate.partial()

The correct method is PromptTemplate.from_template().partial() to create partial prompts.

If a partial prompt fixes variable 'lang', what must you provide when formatting it?

A All other variables except 'lang'

B No variables needed

C Only 'lang' variable

D Variables unrelated to the prompt

You must provide all variables not fixed in the partial prompt when formatting.

What error occurs if you forget to provide a variable when formatting a partial prompt?

A TypeError

B SyntaxError

C No error, it fills with empty string

D KeyError or missing variable error

Missing variables cause a KeyError or similar because the prompt can't be fully formatted.

Partial prompt templates are best described as:

A Templates without any variables

B Templates that generate random text

C Templates with some variables fixed and others open

D Templates that cannot be reused

Partial prompt templates fix some variables and leave others open for later filling.

Explain what a partial prompt template is and why it is useful in Langchain.

Think about building prompts step-by-step.

Describe how you would create and use a partial prompt template to translate text to a fixed language.

Imagine you want to always translate to French but change the text.

Practice

1. What is the main purpose of using PartialPromptTemplate in Langchain?

easy

A. To create reusable parts of prompts that can be filled later

B. To execute a prompt directly without variables

C. To store the final output of a prompt

D. To connect multiple language models together

Solution

1. Step 1: Understand the role of PartialPromptTemplate

   PartialPromptTemplate is designed to hold parts of a prompt with placeholders for variables.

2. Step 2: Recognize its use for reusability

   This allows you to reuse prompt pieces and fill variables later to form a complete prompt.

3. Final Answer:

   To create reusable parts of prompts that can be filled later -> Option A

4. Quick Check:

   PartialPromptTemplate = reusable prompt parts [OK]

Hint: Think reusable prompt pieces filled later [OK]

Common Mistakes:

• Confusing it with final prompt execution
• Thinking it stores output instead of template
• Assuming it connects models directly

2. Which of the following is the correct way to create a PartialPromptTemplate with a variable named name?

easy

A. PartialPromptTemplate(template="Hello {name}")

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

C. PartialPromptTemplate(template="Hello {name}", inputs=["name"])

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

Solution

1. Step 1: Check the required parameters for PartialPromptTemplate

   It requires a template string and a list named input_variables specifying variable names.

2. Step 2: Match the correct syntax

   PartialPromptTemplate(template="Hello {name}", input_variables=["name"]) correctly uses input_variables=["name"] to declare the variable.

3. Final Answer:

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

4. Quick Check:

   Use input_variables list to declare variables [OK]

Hint: Remember input_variables param holds variable names [OK]

Common Mistakes:

• Using wrong parameter names like variables or inputs
• Omitting input_variables list
• Not matching variable names in template and list

3. Given the following code, what will be the output of full_prompt.format(name="Alice")?

from langchain.prompts import PartialPromptTemplate, PromptTemplate
partial = PartialPromptTemplate(template="Hello {name}", input_variables=["name"])
full_prompt = PromptTemplate(template="{greeting}, welcome!", input_variables=["greeting"])
full_prompt = full_prompt.partial(greeting=partial)

medium

A. "{greeting}, welcome!"

B. "Hello Alice, welcome!"

C. "Hello {name}, welcome!"

D. Error: missing variable 'name'

Solution

1. Step 1: Understand partial prompt substitution

   The partial prompt replaces the greeting variable in full_prompt with the partial template.

2. Step 2: Format the full prompt with name="Alice"

   Calling full_prompt.format(name="Alice") fills {name} in partial, producing "Hello Alice", then inserts it into full prompt, resulting in "Hello Alice, welcome!".

3. Final Answer:

   "Hello Alice, welcome!" -> Option B

4. Quick Check:

   Partial fills greeting, then full prompt formats [OK]

Hint: Partial fills variables inside main prompt [OK]

Common Mistakes:

• Expecting raw template string without substitution
• Confusing variable names and placeholders
• Missing that partial is nested inside full prompt

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

partial = PartialPromptTemplate(template="Hi {user}", input_variables=["name"])

medium

A. Variable name in template and input_variables do not match

B. Missing import statement for PartialPromptTemplate

C. Template string must not contain variables

D. input_variables should be a string, not a list

Solution

1. Step 1: Compare template variables and input_variables list

   The template uses {user} but input_variables list contains "name".

2. Step 2: Identify mismatch causes error

   Variables must match exactly; mismatch causes runtime error when formatting.

3. Final Answer:

   Variable name in template and input_variables do not match -> Option A

4. Quick Check:

   Variable names must match in template and input_variables [OK]

Hint: Check variable names match exactly in template and list [OK]

Common Mistakes:

• Assuming variable names can differ
• Ignoring case sensitivity
• Thinking input_variables can be a string

5. You want to build a prompt that greets a user and mentions their favorite color using partial prompt templates. Which approach correctly combines two partial templates greet and color into a full prompt?

hard

A. Create two PartialPromptTemplates but combine by concatenating their templates as strings manually

B. Create one PartialPromptTemplate with all variables: PartialPromptTemplate(template="Hello {name}. Your favorite color is {color}.", input_variables=["name", "color"])

C. Create greet = PartialPromptTemplate(template="Hello {name}", input_variables=["name"]) and color = PartialPromptTemplate(template="Your favorite color is {color}", input_variables=["color"]), then combine with full = PromptTemplate(template="{greeting}. {color_info}.", input_variables=["greeting", "color_info"]) and use full.partial(greeting=greet, color_info=color)

D. Use PromptTemplate only with variables name and color without partial templates

Solution

1. Step 1: Define two partial templates for greeting and color

   Each partial holds a reusable piece with its own variables.

2. Step 2: Combine partials into a full prompt using placeholders

   The full prompt uses placeholders for each partial, then partial() method fills them with partial templates.

3. Step 3: This approach keeps prompts modular and variables scoped

   It allows filling variables later and keeps code organized.

4. Final Answer:

   Create greet = PartialPromptTemplate(template="Hello {name}", input_variables=["name"]) and color = PartialPromptTemplate(template="Your favorite color is {color}", input_variables=["color"]), then combine with full = PromptTemplate(template="{greeting}. {color_info}.", input_variables=["greeting", "color_info"]) and use full.partial(greeting=greet, color_info=color) -> Option C

5. Quick Check:

   Combine partials via placeholders and partial() method [OK]

Hint: Use partial() to nest partial templates inside full prompt [OK]

Common Mistakes:

• Trying to concatenate templates as strings manually
• Using one partial for all variables losing modularity
• Ignoring partial() method for combining templates