Retry parser

While in some cases it is possible to fix any parsing mistakes by only looking at the output, in other cases it isn’t. An example of this is when the output is not just in the incorrect format, but is partially complete. Consider the below example.

from langchain.chat_models import ChatOpenAI
from langchain.llms import OpenAI
from langchain.output_parsers import (
    OutputFixingParser,
    PydanticOutputParser,
)
from langchain.prompts import (
    PromptTemplate,
)
from pydantic import BaseModel, Field

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)

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?')