Transformers are classes that enables data transformation while preprocessing the data for machine learning . Examples of transformer in scikit-learn are SimpleImputer , MinMaxScaler, OrdinalEncoder etc. My transformer won't be transforming a dataset rather it will take in a dataset and it features and also a model to train with, splits the dataset into the number of folds you wish to work with then trains the model. The transformer contains methods for viewing the performance of the model and also making predictions.