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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def orders(self, dt=None):
 """Retrieve the dict-form of all of the orders in a given bar or for the whole simulation. Parameters dt : pd.Timestamp or None, optional The particular datetime to look up order for. If not passed, or None is explicitly passed, all of the orders will be returned. Returns ------- orders : list[dict] The order information. """

        if dt is None:
            # orders by id is already flattened
            return [o.to_dict() for o in itervalues(self._orders_by_id)]

        return [
            o.to_dict()
            for o in itervalues(self._orders_by_modified.get(dt, {}))
        ]