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FIX Avoid fitting a pipeline without steps #31723

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Merged
adrinjalali merged 4 commits into from
Jul 14, 2025
Merged

FIX Avoid fitting a pipeline without steps #31723

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343d19b
avoid empty Pipeline
DeaMariaLeon Jul 4, 2025
391e8f5
Avoid fitting a pipeline without steps
DeaMariaLeon Jul 8, 2025
e54f0c5
Merge remote-tracking branch 'upstream/main' into pipeline
DeaMariaLeon Jul 8, 2025
92bd2a6
clearer message
DeaMariaLeon Jul 8, 2025
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3 changes: 2 additions & 1 deletion sklearn/pipeline.py
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Original file line number Diff line number Diff line change
Expand Up @@ -320,6 +320,8 @@ def set_params(self, **kwargs):
return self

def _validate_steps(self):
if not self.steps:
raise ValueError("The pipeline is empty. Please add steps.")
names, estimators = zip(*self.steps)

# validate names
Expand Down Expand Up @@ -1289,7 +1291,6 @@ def __sklearn_is_fitted__(self):

An empty pipeline is considered fitted.
"""

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@DeaMariaLeon DeaMariaLeon Jul 8, 2025

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Here is where I wanted to to check if the pipeline had steps. But this means the display will fail as well.
And I just saw this: "An empty pipeline is considered fitted." This means that the HTML display is actually correct.

# First find the last step that is not 'passthrough'
last_step = None
for _, estimator in reversed(self.steps):
Expand Down
10 changes: 10 additions & 0 deletions sklearn/tests/test_pipeline.py
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Expand Up @@ -282,6 +282,16 @@ def test_pipeline_invalid_parameters():
assert params == params2


def test_empty_pipeline():
X = iris.data
y = iris.target

pipe = Pipeline([])
msg = "The pipeline is empty. Please add steps."
with pytest.raises(ValueError, match=msg):
pipe.fit(X, y)


def test_pipeline_init_tuple():
# Pipeline accepts steps as tuple
X = np.array([[1, 2]])
Expand Down