重试解析器

在某些情况下，只通过查看输出就可以修复任何解析错误，但在其他情况下则不行。一个例子是当输出不仅格式不正确，而且部分不完整时。考虑下面的例子。

from langchain.prompts import (
    PromptTemplate,
    ChatPromptTemplate,
    HumanMessagePromptTemplate,
)
from langchain.llms import OpenAI
from langchain.chat_models import ChatOpenAI
from langchain.output_parsers import (
    PydanticOutputParser,
    OutputFixingParser,
    RetryOutputParser,
)
from pydantic import BaseModel, Field, validator
from typing import List

template = """Based on the user question, provide an Action and Action Input for what step should be taken.
{format_instructions}
Question: {query}
Response:"""

class Action(BaseModel):
    action: str = Field(description="action to take")
    action_input: str = Field(description="input to the action")

parser = PydanticOutputParser(pydantic_object=Action)

prompt = PromptTemplate(
    template="Answer the user query.\n{format_instructions}\n{query}\n",
    input_variables=["query"],
    partial_variables={"format_instructions": parser.get_format_instructions()},
)

prompt_value = prompt.format_prompt(query="who is leo di caprios gf?")

bad_response = '{"action": "search"}'

parser.parse(bad_response)

如果我们尝试直接解析这个响应，将会出现错误。

parser.parse(bad_response)

ValidationError: 1 validation error for Action
action_input
  field required (type=value_error.missing)

During handling of the above exception, another exception occurred:

OutputParserException: Failed to parse Action from completion {"action": "search"}. Got: 1 validation error for Action
action_input
  field required (type=value_error.missing)

如果我们尝试使用OutputFixingParser来修复这个错误，它会感到困惑 - 也就是说，它不知道实际上应该为动作输入放什么。

fix_parser = OutputFixingParser.from_llm(parser=parser, llm=ChatOpenAI())

fix_parser.parse(bad_response)

Action(action='search', action_input='')

相反，我们可以使用RetryOutputParser，它将提示（以及原始输出）传递给再次尝试获取更好的响应。

from langchain.output_parsers import RetryWithErrorOutputParser

retry_parser = RetryWithErrorOutputParser.from_llm(
    parser=parser, llm=OpenAI(temperature=0)
)

retry_parser.parse_with_prompt(bad_response, prompt_value)

Action(action='search', action_input='who is leo di caprios gf?')