scikit-learn has one of the most carefully designed APIs in all of Python. Once you understand its three object types — estimators, transformers, and pipelines — every model you ever use will feel familiar. This lesson builds that mental model from scratch.
1-A 2-A 3-A 4-A | 5 fit 6 transform 7 = Pipeline([('scaler', StandardScaler()), ('clf', LogisticRegression())]) 8 = Fitting on test data leaks information (data leakage) 9 = Estimator learns/predicts; transformer reshapes features | 10 = fit_transform each step, then fit the final estimator