'Do nothing and return the estimator unchanged
This method is just there to implement the usual API and hence
work in pipelines.
Parameters
X : array-like, shape (n_samples, n_features)
Training vector, where n_samples in the number of samples
and n_features is the number of features.
Returns
self : object
Returns the object itself'

def fit(self, X, y=None):

    return self
