Method _perform_cast

starlette/config.py:123–140

(
        self,
        key: str,
        value: Any,
        cast: Callable[[Any], Any] | None = None,
    )

        return file_values

    def _perform_cast(
        self,
        key: str,
        value: Any,
        cast: Callable[[Any], Any] | None = None,
    ) -> Any:
        if cast is None or value is None:
            return value
        elif cast is bool and isinstance(value, str):
            mapping = {"true": True, "1": True, "false": False, "0": False}
            value = value.lower()
            if value not in mapping:
                raise ValueError(f"Config '{key}' has value '{value}'. Not a valid bool.")
            return mapping[value]
        try:
            return cast(value)
        except (TypeError, ValueError):
            raise ValueError(f"Config '{key}' has value '{value}'. Not a valid {cast.__name__}.")