#custom-transformer

What happens when this code runs?

import numpy as np
from sklearn.base import BaseEstimator, TransformerMixin

class Centerer(TransformerMixin, BaseEstimator):
    def fit(self, X, y=None):
        self.mean_ = X.mean(axis=0)      # no return statement

    def transform(self, X):
        return X - self.mean_

X = np.array([[1.0, 2.0], [3.0, 6.0]])
print(Centerer().fit_transform(X))