【LangChain系列 7】Prompt模版——少样本prompt模版(一)

原文地址：【LangChain系列 7】Prompt模版——少样本prompt模版(一)

本文速读：

• prompt样本集合

• prompt样本选择器

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少样本模版的意思是：在prompt中包含一些样本，这样LLM就可以根据这些样本，更好的理解prompt，从而给出更加符合我们需要的回答。

下面我们将介绍两种方式实现少样本prompt模版：

• prompt样本集合

• prompt样本选择器

01 Prompt样本集合

Prompt样本集合是指：将所有给定的样本集合作为prompt的一部分，输入给LLM。比如说样本如下：

from langchain.prompts.few_shot import FewShotPromptTemplate
from langchain.prompts.prompt import PromptTemplate

examples = [
  {
    "question": "Who lived longer, Muhammad Ali or Alan Turing?",
    "answer": 
"""
Are follow up questions needed here: Yes.
Follow up: How old was Muhammad Ali when he died?
Intermediate answer: Muhammad Ali was 74 years old when he died.
Follow up: How old was Alan Turing when he died?
Intermediate answer: Alan Turing was 41 years old when he died.
So the final answer is: Muhammad Ali
"""
  },
  {
    "question": "When was the founder of craigslist born?",
    "answer": 
"""
Are follow up questions needed here: Yes.
Follow up: Who was the founder of craigslist?
Intermediate answer: Craigslist was founded by Craig Newmark.
Follow up: When was Craig Newmark born?
Intermediate answer: Craig Newmark was born on December 6, 1952.
So the final answer is: December 6, 1952
"""
  },
  {
    "question": "Who was the maternal grandfather of George Washington?",
    "answer":
"""
Are follow up questions needed here: Yes.
Follow up: Who was the mother of George Washington?
Intermediate answer: The mother of George Washington was Mary Ball Washington.
Follow up: Who was the father of Mary Ball Washington?
Intermediate answer: The father of Mary Ball Washington was Joseph Ball.
So the final answer is: Joseph Ball
"""
  },
  {
    "question": "Are both the directors of Jaws and Casino Royale from the same country?",
    "answer":
"""
Are follow up questions needed here: Yes.
Follow up: Who is the director of Jaws?
Intermediate Answer: The director of Jaws is Steven Spielberg.
Follow up: Where is Steven Spielberg from?
Intermediate Answer: The United States.
Follow up: Who is the director of Casino Royale?
Intermediate Answer: The director of Casino Royale is Martin Campbell.
Follow up: Where is Martin Campbell from?
Intermediate Answer: New Zealand.
So the final answer is: No
"""
  }
]

example_prompt = PromptTemplate(input_variables=["question", "answer"], template="Question: {question}\n{answer}")
print(example_prompt.format(**examples[0]))

输出结果：

    Question: Who lived longer, Muhammad Ali or Alan Turing?
    
    Are follow up questions needed here: Yes.
    Follow up: How old was Muhammad Ali when he died?
    Intermediate answer: Muhammad Ali was 74 years old when he died.
    Follow up: How old was Alan Turing when he died?
    Intermediate answer: Alan Turing was 41 years old when he died.
    So the final answer is: Muhammad Ali
    

下面我们创建FewShotPromptTemplate实例，并将所有样本通过参数examples传入给模版：

prompt = FewShotPromptTemplate(
    examples=examples, 
    example_prompt=example_prompt, 
    suffix="Question: {input}", 
    input_variables=["input"]
)

print(prompt.format(input="Who was the father of Mary Ball Washington?"))

输出结果：

    Question: Who lived longer, Muhammad Ali or Alan Turing?
    
    Are follow up questions needed here: Yes.
    Follow up: How old was Muhammad Ali when he died?
    Intermediate answer: Muhammad Ali was 74 years old when he died.
    Follow up: How old was Alan Turing when he died?
    Intermediate answer: Alan Turing was 41 years old when he died.
    So the final answer is: Muhammad Ali
    
    
    Question: When was the founder of craigslist born?
    
    Are follow up questions needed here: Yes.
    Follow up: Who was the founder of craigslist?
    Intermediate answer: Craigslist was founded by Craig Newmark.
    Follow up: When was Craig Newmark born?
    Intermediate answer: Craig Newmark was born on December 6, 1952.
    So the final answer is: December 6, 1952
    
    
    Question: Who was the maternal grandfather of George Washington?
    
    Are follow up questions needed here: Yes.
    Follow up: Who was the mother of George Washington?
    Intermediate answer: The mother of George Washington was Mary Ball Washington.
    Follow up: Who was the father of Mary Ball Washington?
    Intermediate answer: The father of Mary Ball Washington was Joseph Ball.
    So the final answer is: Joseph Ball
    
    
    Question: Are both the directors of Jaws and Casino Royale from the same country?
    
    Are follow up questions needed here: Yes.
    Follow up: Who is the director of Jaws?
    Intermediate Answer: The director of Jaws is Steven Spielberg.
    Follow up: Where is Steven Spielberg from?
    Intermediate Answer: The United States.
    Follow up: Who is the director of Casino Royale?
    Intermediate Answer: The director of Casino Royale is Martin Campbell.
    Follow up: Where is Martin Campbell from?
    Intermediate Answer: New Zealand.
    So the final answer is: No
    
    
    Question: Who was the father of Mary Ball Washington?

以上就是通过 prompt样本集合 的方式创建了少样本prompt模版。

02 Prompt样本选择器

prompt样本集合

将所有的样本作为prompt的一部分，这种方式有两个问题：

1. 有些样本可能和我们的提问的相关性不大

2. 所有的样本太多，超过了LLM的token限制

为了解决这个问题，LangChain提供了ExampleSelector，这样我们就可以选择部分更加合适的样本输入给LLM。

下面我们用SemanticSimilarityExampleSelector重写上面的代码。

1. 定义example_selector

from langchain.prompts.example_selector import SemanticSimilarityExampleSelector
from langchain.vectorstores import Chroma
from langchain.embeddings import OpenAIEmbeddings


example_selector = SemanticSimilarityExampleSelector.from_examples(
    # This is the list of examples available to select from.
    examples,
    # This is the embedding class used to produce embeddings which are used to measure semantic similarity.
    OpenAIEmbeddings(),
    # This is the VectorStore class that is used to store the embeddings and do a similarity search over.
    Chroma,
    # This is the number of examples to produce.
    k=1
)

# Select the most similar example to the input.
question = "Who was the father of Mary Ball Washington?"
selected_examples = example_selector.select_examples({"question": question})
print(f"Examples most similar to the input: {question}")
for example in selected_examples:
    print("\n")
    for k, v in example.items():
        print(f"{k}: {v}")

输出结果为：

    Running Chroma using direct local API.
    Using DuckDB in-memory for database. Data will be transient.
    Examples most similar to the input: Who was the father of Mary Ball Washington?
    
    
    question: Who was the maternal grandfather of George Washington?
    answer: 
    Are follow up questions needed here: Yes.
    Follow up: Who was the mother of George Washington?
    Intermediate answer: The mother of George Washington was Mary Ball Washington.
    Follow up: Who was the father of Mary Ball Washington?
    Intermediate answer: The father of Mary Ball Washington was Joseph Ball.
    So the final answer is: Joseph Ball
    

2. 创建FewShotPromptTemplate实例

prompt = FewShotPromptTemplate(
    example_selector=example_selector, 
    example_prompt=example_prompt, 
    suffix="Question: {input}", 
    input_variables=["input"]
)

print(prompt.format(input="Who was the father of Mary Ball Washington?"))

输出结果：

    Question: Who was the maternal grandfather of George Washington?
    
    Are follow up questions needed here: Yes.
    Follow up: Who was the mother of George Washington?
    Intermediate answer: The mother of George Washington was Mary Ball Washington.
    Follow up: Who was the father of Mary Ball Washington?
    Intermediate answer: The father of Mary Ball Washington was Joseph Ball.
    So the final answer is: Joseph Ball
    
    
    Question: Who was the father of Mary Ball Washington?

通过ExampleSelector的方式选择合适的部分样本作为prompt的一部分，这种方式称为 prompt样本选择器 ，一方面解决样本过多的问题，另一方面可以提高prompt的质量，从而得到更加符合我们要求的回答。

本文小结

通过介绍 prompt样本集合 和 prompt样本选择器两种创建少样本prompt模版的方式，我们对 少样本prompt模版 有了基本的认识，可以根据实际的业务需求创建自己的少样本prompt模版了。