An asset is restricted for all dts if it is in the static list.

def is_restricted(self, assets, dt):
        """
        An asset is restricted for all dts if it is in the static list.
        """
        if isinstance(assets, Asset):
            return assets in self._restricted_set
        return pd.Series(
            index=pd.Index(assets),
            data=vectorized_is_element(assets, self._restricted_set)
        )