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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 get_items_by_banks(self, bank_ids):
 """Gets the list of ``Items`` corresponding to a list of ``Banks``. arg: bank_ids (osid.id.IdList):
 list of bank ``Ids`` return: (osid.assessment.ItemList) - list of items raise: NullArgument - ``bank_ids`` is ``null`` raise: OperationFailed - unable to complete request raise: PermissionDenied - assessment failure *compliance: mandatory -- This method must be implemented.* """

        # Implemented from template for
        # osid.resource.ResourceBinSession.get_resources_by_bins
        item_list = []
        for bank_id in bank_ids:
            item_list += list(
                self.get_items_by_bank(bank_id))
        return objects.ItemList(item_list)