old_contents: from Orange.base import Learner, Model, SklLearner, SklModel
  
  __all__ = ["LearnerRegression", "ModelRegression",
             "SklModelRegression", "SklLearnerRegression"]
  
  
  class LearnerRegression(Learner):
      learner_adequacy_err_msg = "Continuous class variable expected."
  
      def check_learner_adequacy(self, domain):
          return domain.has_continuous_class
  
  
  class ModelRegression(Model):
      pass
  
  
  class SklLearnerRegression(SklLearner, LearnerRegression):
      pass
  
  
  class SklModelRegression(SklModel, ModelRegression):
      pass
  
new_contents: from Orange.base import Learner, Model, SklLearner, SklModel
  
  __all__ = ["LearnerRegression", "ModelRegression",
             "SklModelRegression", "SklLearnerRegression"]
  
  
  class LearnerRegression(Learner):
      learner_adequacy_err_msg = "Continuous class variable expected."
  
      def check_learner_adequacy(self, domain):
          return domain.has_continuous_class
  
  
  class ModelRegression(Model):
      pass
  
  
  class SklModelRegression(SklModel, ModelRegression):
      pass
  
  
  class SklLearnerRegression(SklLearner, LearnerRegression):
      __returns__ = SklModelRegression
  
subject: Use the appropriate Model base class