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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 create_from_lambda_arn(cls, client, lambda_arn):
 # type: (TypedAWSClient, str) -> LogRetriever """Create a LogRetriever from a client and lambda arn. :type client: botocore.client.Logs :param client: A ``logs`` client. :type lambda_arn: str :param lambda_arn: The ARN of the lambda function. :return: An instance of ``LogRetriever``. """

        lambda_name = lambda_arn.split(':')[6]
        log_group_name = '/aws/lambda/%s' % lambda_name
        return cls(client, log_group_name)