check_fit_idempotent

yohou.testing.transformer.check_fit_idempotent(transformer, X, y=None)

Check that fit(X).fit(X) equals fit(X).

Calling fit multiple times with same data should yield identical internal state and predictions.

Parameters

Name	Type	Description	Default
transformer	BaseTransformer	Unfitted transformer	required
X	DataFrame	Training data	required
y	DataFrame	Target data for supervised transformers	None

Raises

Type	Description
AssertionError	If double-fit produces different results

Source Code

View on GitHub

Show/Hide source

def check_fit_idempotent(transformer, X: pl.DataFrame, y: pl.DataFrame | None = None) -> None:
    """Check that fit(X).fit(X) equals fit(X).

    Calling fit multiple times with same data should yield identical
    internal state and predictions.

    Parameters
    ----------
    transformer : BaseTransformer
        Unfitted transformer
    X : pl.DataFrame
        Training data
    y : pl.DataFrame, optional
        Target data for supervised transformers

    Raises
    ------
    AssertionError
        If double-fit produces different results

    """
    transformer1 = clone(transformer)
    transformer2 = clone(transformer)

    # Single fit
    transformer1.fit(X, y)
    X_trans1 = transformer1.transform(X)

    # Double fit
    transformer2.fit(X, y).fit(X, y)
    X_trans2 = transformer2.transform(X)

    assert_frame_equal(X_trans1, X_trans2, rel_tol=1e-5, abs_tol=1e-8)

    # Check fitted attributes match
    for attr in ["feature_names_in_", "n_features_in_", "_observation_horizon"]:
        if hasattr(transformer1, attr):
            val1 = getattr(transformer1, attr)
            val2 = getattr(transformer2, attr)
            assert val1 == val2, f"Attribute '{attr}' differs after double fit: {val1} vs {val2}"