codekingpro/portable-devtools

1"""Utilities for formatting strings."""2 3from collections.abc import Mapping, Sequence4from string import Formatter5from typing import Any6 7 8class StrictFormatter(Formatter):9    """A string formatter that enforces keyword-only argument substitution.10 11    This formatter extends Python's built-in `string.Formatter` to provide stricter12    validation for prompt template formatting. It ensures that all variable13    substitutions use keyword arguments rather than positional arguments, which improves14    clarity and reduces errors when formatting prompt templates.15 16    Example:17        >>> fmt = StrictFormatter()18        >>> fmt.format("Hello, {name}!", name="World")19        'Hello, World!'20        >>> fmt.format("Hello, {}!", "World")  # Raises ValueError21    """22 23    def vformat(24        self, format_string: str, args: Sequence, kwargs: Mapping[str, Any]25    ) -> str:26        """Format a string using only keyword arguments.27 28        Overrides the base `vformat` to reject positional arguments, ensuring all29        substitutions are explicit and named.30 31        Args:32            format_string: A string containing replacement fields (e.g., `'{name}'`).33            args: Positional arguments (must be empty).34            kwargs: Keyword arguments for substitution into the format string.35 36        Returns:37            The formatted string with all replacement fields substituted.38 39        Raises:40            ValueError: If any positional arguments are provided.41        """42        if len(args) > 0:43            msg = (44                "No arguments should be provided, "45                "everything should be passed as keyword arguments."46            )47            raise ValueError(msg)48        return super().vformat(format_string, args, kwargs)49 50    def validate_input_variables(51        self, format_string: str, input_variables: list[str]52    ) -> None:53        """Validate that input variables match the placeholders in a format string.54 55        Checks that the provided input variables can be used to format the given string56        without missing or extra keys. This is useful for validating prompt templates57        before runtime.58 59        Args:60            format_string: A string containing replacement fields to validate61                against (e.g., `'Hello, {name}!'`).62            input_variables: List of variable names expected to fill the63                replacement fields.64 65        Raises:66            KeyError: If the format string contains placeholders not present67                in input_variables.68 69        Example:70            >>> fmt = StrictFormatter()71            >>> fmt.validate_input_variables("Hello, {name}!", ["name"])  # OK72            >>> fmt.validate_input_variables("Hello, {name}!", ["other"])  # Raises73        """74        dummy_inputs = dict.fromkeys(input_variables, "foo")75        super().format(format_string, **dummy_inputs)76 77 78#: Default StrictFormatter instance for use throughout LangChain.79#: Used internally for formatting prompt templates with named variables.80formatter = StrictFormatter()81