重试解析器

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

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"}'

If we try to parse this response as is, we will get an error

parser.parse(bad_response)

---------------------------------------------------------------------------

ValidationError                           Traceback (most recent call last)

File ~/workplace/langchain/langchain/output_parsers/pydantic.py:24, in PydanticOutputParser.parse(self, text)
     23     json_object = json.loads(json_str)
---> 24     return self.pydantic_object.parse_obj(json_object)
     26 except (json.JSONDecodeError, ValidationError) as e:


File ~/.pyenv/versions/3.9.1/envs/langchain/lib/python3.9/site-packages/pydantic/main.py:527, in pydantic.main.BaseModel.parse_obj()


File ~/.pyenv/versions/3.9.1/envs/langchain/lib/python3.9/site-packages/pydantic/main.py:342, in pydantic.main.BaseModel.__init__()


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


During handling of the above exception, another exception occurred:


OutputParserException                     Traceback (most recent call last)

Cell In[6], line 1
----> 1 parser.parse(bad_response)


File ~/workplace/langchain/langchain/output_parsers/pydantic.py:29, in PydanticOutputParser.parse(self, text)
     27 name = self.pydantic_object.__name__
     28 msg = f"Failed to parse {name} from completion {text}. Got: {e}"
---> 29 raise OutputParserException(msg)


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

If we try to use the OutputFixingParser to fix this error, it will be confused - namely, it doesn't know what to actually put for action input.

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

fix_parser.parse(bad_response)

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

Instead, we can use the RetryOutputParser, which passes in the prompt (as well as the original output) to try again to get a better response.

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?')