code: def transformer(y, func=None):
      """Transforms target variable and prediction"""
      if func is None:
          return y
      else:
          return func(y)
  
file_path: vecstack/vecstack/core.py
imports: from __future__ import print_function
  from __future__ import division
  import os
  import sys
  import warnings
  from datetime import datetime
  import numpy
  import scipy.stats
  from sklearn.model_selection import KFold
  from sklearn.model_selection import StratifiedKFold
  from sklearn.metrics import mean_absolute_error
  from sklearn.metrics import accuracy_score
  from sklearn.metrics import log_loss
  from sklearn.utils.validation import check_X_y
  from sklearn.utils.validation import check_array
  from sklearn.base import clone
label_desc: Use image node_id 1 for calling a global function with example usage: transformer(y, func) and returns: y, func