'Purchases a reserved DB instance offering.
:type reserved_db_instances_offering_id: string
:param reserved_db_instances_offering_id: The ID of the Reserved DB
instance offering to purchase.
Example: 438012d3-4052-4cc7-b2e3-8d3372e0e706
:type reserved_db_instance_id: string
:param reserved_db_instance_id: Customer-specified identifier to track
this reservation.
Example: myreservationID
:type db_instance_count: integer
:param db_instance_count: The number of instances to reserve.
Default: `1`
:type tags: list
:param tags: A list of tags. Tags must be passed as tuples in the form
[(\'key1\', \'valueForKey1\'), (\'key2\', \'valueForKey2\')]'

def purchase_reserved_db_instances_offering(self, reserved_db_instances_offering_id, reserved_db_instance_id=None, db_instance_count=None, tags=None):

    params = {'ReservedDBInstancesOfferingId': reserved_db_instances_offering_id}
    if (reserved_db_instance_id is not None):
        params['ReservedDBInstanceId'] = reserved_db_instance_id
    if (db_instance_count is not None):
        params['DBInstanceCount'] = db_instance_count
    if (tags is not None):
        self.build_complex_list_params(params, tags, 'Tags.member', ('Key', 'Value'))
    return self._make_request(action='PurchaseReservedDBInstancesOffering', verb='POST', path='/', params=params)
