Exception class to raise if estimator is used before fitting.
This class inherits from both ValueError and AttributeError to help with exception handling and backward compatibility.
>>> from sklearn.svm import LinearSVC
>>> from sklearn.exceptions import NotFittedError
>>> try:
... LinearSVC().predict([[1, 2], [2, 3], [3, 4]])
... except NotFittedError as e:
... print(repr(e))
NotFittedError("This LinearSVC instance is not fitted yet. Call 'fit' with
appropriate arguments before using this estimator."...)
Changed in version 0.18: Moved from sklearn.utils.validation.
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https://scikit-learn.org/1.6/modules/generated/sklearn.exceptions.NotFittedError.html