code: def fit(self, X, y=None, **fit_params):
          
          self._check_params()
  
          cv = check_cv(self.cv, X)
          self._fit(X, y, cv, **fit_params)
  
          return self
docs: Fit ensemble of models
  
          Parameters
          ----------
          X : array-like, shape = (n_samples, n_features)
              Training data.
  
          y : array-like, optional
              Target data if base estimators are supervised.
  
          Returns
          -------
          self