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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 list(self):
 """List Reserved Capacities"""

        mask = """mask[availableInstanceCount, occupiedInstanceCount,
instances[id, billingItem[description, hourlyRecurringFee]], instanceCount, backendRouter[datacenter]]"""
        results = self.client.call('Account', 'getReservedCapacityGroups', mask=mask)
        return results