def get_parameters_at_instant(self, instant):
        """
        Get the parameters of the legislation at a given instant

        :param instant: string of the format 'YYYY-MM-DD' or `openfisca_core.periods.Instant` instance.
        :returns: The parameters of the legislation at a given instant.
        :rtype: :any:`ParameterNodeAtInstant`
        """
        if isinstance(instant, periods.Period):
            instant = instant.start
        elif isinstance(instant, (str, int)):
            instant = periods.instant(instant)
        else:
            assert isinstance(instant, periods.Instant), "Expected an Instant (e.g. Instant((2017, 1, 1)) ). Got: {}.".format(instant)

        parameters_at_instant = self._parameters_at_instant_cache.get(instant)
        if parameters_at_instant is None and self.parameters is not None:
            parameters_at_instant = self.parameters.get_at_instant(str(instant))
            self._parameters_at_instant_cache[instant] = parameters_at_instant
        return parameters_at_instant
Get the parameters of the legislation at a given instant

        :param instant: string of the format 'YYYY-MM-DD' or `openfisca_core.periods.Instant` instance.
        :returns: The parameters of the legislation at a given instant.
        :rtype: :any:`ParameterNodeAtInstant`