src/mozanalysis/metrics.py [129:149]:
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    @default_dataset.validator
    def _check_default_dataset_provided_if_needed(self, attribute, value):
        self.from_expr_for(None)

    def from_expr_for(self, dataset: str | None) -> str:
        """Expands the ``from_expr`` template for the given dataset.
        If ``from_expr`` is not a template, returns ``from_expr``.

        Args:
            dataset (str or None): Dataset name to substitute
                into the from expression.
        """
        effective_dataset = dataset or self.default_dataset
        if effective_dataset is None:
            try:
                return self._from_expr.format()
            except Exception as e:
                raise ValueError(
                    f"{self.name}: from_expr contains a dataset template but no value was provided."  # noqa:E501
                ) from e
        return self._from_expr.format(dataset=effective_dataset)
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src/mozanalysis/segments.py [61:81]:
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    @default_dataset.validator
    def _check_default_dataset_provided_if_needed(self, attribute, value):
        self.from_expr_for(None)

    def from_expr_for(self, dataset: str | None) -> str:
        """Expands the ``from_expr`` template for the given dataset.
        If ``from_expr`` is not a template, returns ``from_expr``.

        Args:
            dataset (str or None): Dataset name to substitute
                into the from expression.
        """
        effective_dataset = dataset or self.default_dataset
        if effective_dataset is None:
            try:
                return self._from_expr.format()
            except Exception as e:
                raise ValueError(
                    f"{self.name}: from_expr contains a dataset template but no value was provided."  # noqa:E501
                ) from e
        return self._from_expr.format(dataset=effective_dataset)
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