scikit-learn partial_fit inconsistency and NotFittedError

NotFittedError: 'This scikit-learn model is not fitted yet' when partial_fit not supported

0 reputation · 21 Jan 2026, 04:11 UTC

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The NotFittedError with message 'This scikit-learn model is not fitted yet' is raised when calling predict or score on an estimator that has not been fitted, as documented in the scikit-learn reference.

Not all estimators implement the partial_fit method, creating an unclear API for incremental learning; LinearRegression lacks it while SGDClassifier supports it.

Which scikit-learn estimators currently support partial_fit and which raise NotFittedError on predict calls? How should developers reliably perform online training when estimator capabilities vary?

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NotFittedError: 'This scikit-learn model is not fitted yet' when partial_fit not supported

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