'Cancel the specified Spot Instance Requests.
:type request_ids: list
:param request_ids: A list of strings of the Request IDs to terminate
:type dry_run: bool
:param dry_run: Set to True if the operation should not actually run.
:rtype: list
:return: A list of the instances terminated'

def cancel_spot_instance_requests(self, request_ids, dry_run=False):

    params = {}
    if request_ids:
        self.build_list_params(params, request_ids, 'SpotInstanceRequestId')
    if dry_run:
        params['DryRun'] = 'true'
    return self.get_list('CancelSpotInstanceRequests', params, [('item', SpotInstanceRequest)], verb='POST')
