PydanticOutputParser Class — langchain Architecture

Architecture documentation for the PydanticOutputParser class in pydantic.py from the langchain codebase.

Class python OutputParsing

Entity Profile

OutputParsing→ PydanticOutputParser Class — langchain Architecture

Dependency Diagram

graph TD
  570792b6_910c_5259_8419_5183ac1b1409["PydanticOutputParser"]
  0d9a7db1_a024_a63e_d6da_4108a6cd2019["JsonOutputParser"]
  570792b6_910c_5259_8419_5183ac1b1409 -->|extends| 0d9a7db1_a024_a63e_d6da_4108a6cd2019
  00fb336c_8832_626d_1bf9_f4f07a04d663["pydantic.py"]
  570792b6_910c_5259_8419_5183ac1b1409 -->|defined in| 00fb336c_8832_626d_1bf9_f4f07a04d663
  fd96632b_d191_0274_eb13_17083eb19c1d["_parse_obj()"]
  570792b6_910c_5259_8419_5183ac1b1409 -->|method| fd96632b_d191_0274_eb13_17083eb19c1d
  be3b196e_4a79_f447_3f29_9d15eee5575b["_parser_exception()"]
  570792b6_910c_5259_8419_5183ac1b1409 -->|method| be3b196e_4a79_f447_3f29_9d15eee5575b
  832ab0e8_f54d_dc1d_0342_eccf5c13bd0d["parse_result()"]
  570792b6_910c_5259_8419_5183ac1b1409 -->|method| 832ab0e8_f54d_dc1d_0342_eccf5c13bd0d
  72590bc9_9c62_cc76_ee87_a0199ef2338a["parse()"]
  570792b6_910c_5259_8419_5183ac1b1409 -->|method| 72590bc9_9c62_cc76_ee87_a0199ef2338a
  6bf20b4d_d595_a2e8_9a0a_c828bb0760ad["get_format_instructions()"]
  570792b6_910c_5259_8419_5183ac1b1409 -->|method| 6bf20b4d_d595_a2e8_9a0a_c828bb0760ad
  94c3b392_5e98_e89a_9d75_c0205476adf6["_type()"]
  570792b6_910c_5259_8419_5183ac1b1409 -->|method| 94c3b392_5e98_e89a_9d75_c0205476adf6
  d8e29480_6c2f_f821_c933_dec496874a87["OutputType()"]
  570792b6_910c_5259_8419_5183ac1b1409 -->|method| d8e29480_6c2f_f821_c933_dec496874a87

Relationship Graph

Source Code

libs/core/langchain_core/output_parsers/pydantic.py lines 19–121

class PydanticOutputParser(JsonOutputParser, Generic[TBaseModel]):
    """Parse an output using a Pydantic model."""

    pydantic_object: Annotated[type[TBaseModel], SkipValidation()]
    """The Pydantic model to parse."""

    def _parse_obj(self, obj: dict) -> TBaseModel:
        try:
            if issubclass(self.pydantic_object, pydantic.BaseModel):
                return self.pydantic_object.model_validate(obj)
            if issubclass(self.pydantic_object, pydantic.v1.BaseModel):
                return self.pydantic_object.parse_obj(obj)
            msg = f"Unsupported model version for PydanticOutputParser: \
                        {self.pydantic_object.__class__}"
            raise OutputParserException(msg)
        except (pydantic.ValidationError, pydantic.v1.ValidationError) as e:
            raise self._parser_exception(e, obj) from e

    def _parser_exception(
        self, e: Exception, json_object: dict
    ) -> OutputParserException:
        json_string = json.dumps(json_object, ensure_ascii=False)
        name = self.pydantic_object.__name__
        msg = f"Failed to parse {name} from completion {json_string}. Got: {e}"
        return OutputParserException(msg, llm_output=json_string)

    @overload
    def parse_result(
        self, result: list[Generation], *, partial: Literal[False] = False
    ) -> TBaseModel: ...

    @overload
    def parse_result(
        self, result: list[Generation], *, partial: bool = False
    ) -> TBaseModel | None: ...

    def parse_result(
        self, result: list[Generation], *, partial: bool = False
    ) -> TBaseModel | None:
        """Parse the result of an LLM call to a Pydantic object.

        Args:
            result: The result of the LLM call.
            partial: Whether to parse partial JSON objects.

                If `True`, the output will be a JSON object containing all the keys that
                have been returned so far.

        Raises:
            OutputParserException: If the result is not valid JSON or does not conform
                to the Pydantic model.

        Returns:
            The parsed Pydantic object.
        """
        try:
            json_object = super().parse_result(result)
            return self._parse_obj(json_object)
        except OutputParserException:
            if partial:
                return None
            raise

    def parse(self, text: str) -> TBaseModel:
        """Parse the output of an LLM call to a Pydantic object.

        Args:
            text: The output of the LLM call.

        Returns:
            The parsed Pydantic object.
        """
        return self.parse_result([Generation(text=text)])

    def get_format_instructions(self) -> str:
        """Return the format instructions for the JSON output.

        Returns:
            The format instructions for the JSON output.
        """
        # Copy schema to avoid altering original Pydantic schema.