code: def get_default_target_names(estimator, num_targets=None):
      
      if num_targets is None:
          if len(estimator.coef_.shape) <= 1:
              num_targets = 1
          else:
              num_targets, _ = estimator.coef_.shape
      if num_targets == 1:
          target_names = ['y']
      else:
          target_names = ['y%d' % i for i in range(num_targets)]
      return np.array(target_names)
docs: Return a vector of target names: "y" if there is only one target,
      and "y0", "y1", ... if there are multiple targets.