def _fit(self, X, y, max_samples, max_depth=None, sample_weight=None):
        """Build a Bagging ensemble of estimators from the training
           set (X, y).

        Parameters
        ----------
        X : {array-like, sparse matrix} of shape = [n_samples, n_features]
            The training input samples. Sparse matrices are accepted only if
            they are supported by the base estimator.

        y : array-like, shape = [n_samples]
            The target values (class labels in classification, real numbers in
            regression).

        max_samples : int or float, optional (default=None)
            Argument to use instead of self.max_samples.

        max_depth : int, optional (default=None)
            Override value used when constructing base estimator. Only
            supported if the base estimator has a max_depth parameter.

        sample_weight : array-like, shape = [n_samples] or None
            Sample weights. If None, then samples are equally weighted.
            Note that this is supported only if the base estimator supports
            sample weighting.

        Returns
        -------
        self : object
            Returns self.
        """
        random_state = check_random_state(self.random_state)

        # Convert data
        X, y = check_X_y(X, y, ['csr', 'csc'])

        # Remap output
        n_samples, self.n_features_ = X.shape
        y = self._validate_y(y)

        # Check parameters
        self._validate_estimator()

        if max_depth is not None:
            self.base_estimator_.max_depth = max_depth

        # if max_samples is float:
        if not isinstance(max_samples, (numbers.Integral, np.integer)):
            max_samples = int(max_samples * X.shape[0])

        if not (0 < max_samples <= X.shape[0]):
            raise ValueError("max_samples must be in (0, n_samples]")

        if isinstance(self.max_features, (numbers.Integral, np.integer)):
            max_features = self.max_features
        else:  # float
            max_features = int(self.max_features * self.n_features_)

        if not (0 < max_features <= self.n_features_):
            raise ValueError("max_features must be in (0, n_features]")

        if not self.bootstrap and self.oob_score:
            raise ValueError("Out of bag estimation only available"
                             " if bootstrap=True")

        if self.warm_start and self.oob_score:
            raise ValueError("Out of bag estimate only available"
                             " if warm_start=False")

        if hasattr(self, "oob_score_") and self.warm_start:
            del self.oob_score_

        if not self.warm_start or len(self.estimators_) == 0:
            # Free allocated memory, if any
            self.estimators_ = []
            self.estimators_samples_ = []
            self.estimators_features_ = []

        n_more_estimators = self.n_estimators - len(self.estimators_)

        if n_more_estimators < 0:
            raise ValueError('n_estimators=%d must be larger or equal to '
                             'len(estimators_)=%d when warm_start==True'
                             % (self.n_estimators, len(self.estimators_)))

        elif n_more_estimators == 0:
            warn("Warm-start fitting without increasing n_estimators does not "
                 "fit new trees.")
            return self

        # Parallel loop
        n_jobs, n_estimators, starts = _partition_estimators(n_more_estimators,
                                                             self.n_jobs)
        total_n_estimators = sum(n_estimators)

        # Advance random state to state after training
        # the first n_estimators
        if self.warm_start and len(self.estimators_) > 0:
            random_state.randint(MAX_INT, size=len(self.estimators_))

        seeds = random_state.randint(MAX_INT, size=n_more_estimators)

        all_results = Parallel(n_jobs=n_jobs, verbose=self.verbose)(
            delayed(_parallel_build_estimators)(
                n_estimators[i],
                self,
                X,
                y,
                sample_weight,
                max_samples,
                seeds[starts[i]:starts[i + 1]],
                total_n_estimators,
                verbose=self.verbose)
            for i in range(n_jobs))

        # Reduce
        self.estimators_ += list(itertools.chain.from_iterable(
            t[0] for t in all_results))
        self.estimators_samples_ += list(itertools.chain.from_iterable(
            t[1] for t in all_results))
        self.estimators_features_ += list(itertools.chain.from_iterable(
            t[2] for t in all_results))

        if self.oob_score:
            self._set_oob_score(X, y)

        return self
dataset/ETHPy150Open scikit-learn/scikit-learn/sklearn/ensemble/bagging.py/BaseBagging._fit/original