Pipeline score broken for unsupervised algorithms #4063
Description
The score method for pipeline assigns y=None and always passes it to the score method of the final estimator, but some estimators (for instance KMeans) take only X. Is there a reason to use y=None instead of *args?
Reproducible by
import numpy as np,sklearn
from sklearn.pipeline import Pipeline
from sklearn.cluster import KMeans
X=np.random.rand(100,2)
p=Pipeline([('clf',KMeans(n_clusters=3))])
p.fit(X)
p.score(X)