test_base_transform_output_parser() — langchain Function Reference

Source Code

libs/core/tests/unit_tests/output_parsers/test_base_parsers.py lines 53–93

def test_base_transform_output_parser() -> None:
    """Test base transform output parser."""

    class StrInvertCase(BaseTransformOutputParser[str]):
        """An example parser that inverts the case of the characters in the message."""

        def parse(self, text: str) -> str:
            """Parse a single string into a specific format."""
            raise NotImplementedError

        @override
        def parse_result(
            self, result: list[Generation], *, partial: bool = False
        ) -> str:
            """Parse a list of model Generations into a specific format.

            Args:
                result: A list of `Generation` to be parsed. The Generations are assumed
                    to be different candidate outputs for a single model input.
                    Many parsers assume that only a single generation is passed it in.
                    We will assert for that
                partial: Whether to allow partial results. This is used for parsers
                         that support streaming
            """
            if len(result) != 1:
                msg = "This output parser can only be used with a single generation."
                raise NotImplementedError(msg)
            generation = result[0]
            if not isinstance(generation, ChatGeneration):
                # Say that this one only works with chat generations
                msg = "This output parser can only be used with a chat generation."
                raise OutputParserException(msg)
            content = generation.message.content
            assert isinstance(content, str)
            return content.swapcase()

    model = GenericFakeChatModel(messages=iter([AIMessage(content="hello world")]))
    chain = model | StrInvertCase()
    # inputs to models are ignored, response is hard-coded in model definition
    chunks = list(chain.stream(""))
    assert chunks == ["HELLO", " ", "WORLD"]