controller.py

    def get_voucher(self, number):
        return self.incorporate_transient_state(
            self.store.get(number),
        )

    def incorporate_transient_state(self, voucher):
        """
        Create a new ``Voucher`` which represents the given voucher but which also
        incorporates relevant transient state known to the controller.  For
        example, if a redemption attempt is current in progress, this is
        incorporated.
        """
        if isinstance(voucher.state, model_Pending):
            if voucher.number in self._active:
                return attr.evolve(
                    voucher,
                    state=self._active[voucher.number],
                )
            if voucher.number in self._unpaid:
                return attr.evolve(
                    voucher,
                    state=model_Unpaid(finished=self._unpaid[voucher.number]),
                )
            if voucher.number in self._error:
                return attr.evolve(
                    voucher,
                    state=self._error[voucher.number],
                )
        return voucher


def get_redeemer(plugin_name, node_config, announcement, reactor):
    section_name = u"storageclient.plugins.{}".format(plugin_name)
    redeemer_kind = node_config.get_config(
        section=section_name,
        option=u"redeemer",
        default=u"ristretto",
    )
    return _REDEEMERS[redeemer_kind](section_name, node_config, announcement, reactor)


_REDEEMERS = {
    u"non": NonRedeemer.make,
    u"dummy": DummyRedeemer.make,
    u"double-spend": DoubleSpendRedeemer.make,
    u"unpaid": UnpaidRedeemer.make,
    u"error": ErrorRedeemer.make,
    u"ristretto": RistrettoRedeemer.make,
}


@inlineCallbacks
def bracket(first, last, between):
    """
    Invoke an action between two other actions.

    :param first: A no-argument function that may return a Deferred.  It is
        called first.

    :param last: A no-argument function that may return a Deferred.  It is
        called last.

    :param between: A no-argument function that may return a Deferred.  It is
        called after ``first`` is done and completes before ``last`` is called.

    :return Deferred: A ``Deferred`` which fires with the result of
        ``between``.
    """
    yield first()
    try:
        result = yield between()
    except GeneratorExit:
        raise
    except:
        info = exc_info()
        yield last()
        raise info[0], info[1], info[2]
    else:
        yield last()
        returnValue(result)