FewShotPromptTemplate Class — langchain Architecture

Source Code

libs/core/langchain_core/prompts/few_shot.py lines 120–252

class FewShotPromptTemplate(_FewShotPromptTemplateMixin, StringPromptTemplate):
    """Prompt template that contains few shot examples."""

    @classmethod
    def is_lc_serializable(cls) -> bool:
        """Return `False` as this class is not serializable."""
        return False

    validate_template: bool = False
    """Whether or not to try validating the template."""

    example_prompt: PromptTemplate
    """`PromptTemplate` used to format an individual example."""

    suffix: str
    """A prompt template string to put after the examples."""

    example_separator: str = "\n\n"
    """String separator used to join the prefix, the examples, and suffix."""

    prefix: str = ""
    """A prompt template string to put before the examples."""

    template_format: Literal["f-string", "jinja2"] = "f-string"
    """The format of the prompt template.

    Options are: `'f-string'`, `'jinja2'`.
    """

    def __init__(self, **kwargs: Any) -> None:
        """Initialize the few shot prompt template."""
        if "input_variables" not in kwargs and "example_prompt" in kwargs:
            kwargs["input_variables"] = kwargs["example_prompt"].input_variables
        super().__init__(**kwargs)

    @model_validator(mode="after")
    def template_is_valid(self) -> Self:
        """Check that prefix, suffix, and input variables are consistent."""
        if self.validate_template:
            check_valid_template(
                self.prefix + self.suffix,
                self.template_format,
                self.input_variables + list(self.partial_variables),
            )
        elif self.template_format:
            self.input_variables = [
                var
                for var in get_template_variables(
                    self.prefix + self.suffix, self.template_format
                )
                if var not in self.partial_variables
            ]
        return self

    model_config = ConfigDict(
        arbitrary_types_allowed=True,
        extra="forbid",
    )

    def format(self, **kwargs: Any) -> str:
        """Format the prompt with inputs generating a string.

        Use this method to generate a string representation of a prompt.

        Args:
            **kwargs: Keyword arguments to use for formatting.

        Returns:
            A string representation of the prompt.
        """
        kwargs = self._merge_partial_and_user_variables(**kwargs)
        # Get the examples to use.
        examples = self._get_examples(**kwargs)
        examples = [
            {k: e[k] for k in self.example_prompt.input_variables} for e in examples
        ]
        # Format the examples.
        example_strings = [
            self.example_prompt.format(**example) for example in examples
        ]
        # Create the overall template.