scikit-learn
Standard Python library for classical ML, built on a unified estimator API.
- fit/predict/transform/score across every model.
- Pipelines, GridSearchCV, CV work generically.
- Design pattern imitated by xgboost, lightgbm, etc.
When to use: Tabular ML; classical algorithms; production-ready baselines.
Example: clf = LogisticRegression(); clf.fit(X_train, y_train); clf.score(X_test, y_test).