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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_aws_metric(table_name, lookback_window_start, lookback_period, metric_name):
 """ Returns a metric list from the AWS CloudWatch service, may return None if no metric exists :type table_name: str :param table_name: Name of the DynamoDB table :type lookback_window_start: int :param lookback_window_start: How many minutes to look at :type lookback_period: int :type lookback_period: Length of the lookback period in minutes :type metric_name: str :param metric_name: Name of the metric to retrieve from CloudWatch :returns: list -- A list of time series data for the given metric, may be None if there was no data """

    try:
        now = datetime.utcnow()
        start_time = now - timedelta(minutes=lookback_window_start)
        end_time = now - timedelta(
            minutes=lookback_window_start - lookback_period)

        return cloudwatch_connection.get_metric_statistics(
            period=lookback_period * 60,
            start_time=start_time,
            end_time=end_time,
            metric_name=metric_name,
            namespace='AWS/DynamoDB',
            statistics=['Sum'],
            dimensions={'TableName': table_name},
            unit='Count')
    except BotoServerError as error:
        logger.error(
            'Unknown boto error. Status: "{0}". '
            'Reason: "{1}". Message: {2}'.format(
                error.status,
                error.reason,
                error.message))
        raise