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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_system(model_folder):
 """Return the preprocessing description, the feature description and the model description."""


    # Get model description
    model_description_file = os.path.join(model_folder, "info.yml")
    if not os.path.isfile(model_description_file):
        logging.error("You are probably not in the folder of a model, because "
                      "%s is not a file. (-m argument)",
                      model_description_file)
        sys.exit(-1)
    with open(model_description_file, 'r') as ymlfile:
        model_desc = yaml.load(ymlfile)

    # Get the feature and the preprocessing description
    feature_desc = _get_description(model_desc)
    preprocessing_desc = _get_description(feature_desc)

    return (preprocessing_desc, feature_desc, model_desc)