code: def check_preprocessor(self):
      
      if _is_arraylike(self.preprocessor):
        self.preprocessor_ = ArrayIndexer(self.preprocessor)
      elif callable(self.preprocessor) or self.preprocessor is None:
        self.preprocessor_ = self.preprocessor
      else:
        raise ValueError("Invalid type for the preprocessor: {}. You should "
                         "provide either None, an array-like object, "
                         "or a callable.".format(type(self.preprocessor)))
docs: Initializes the preprocessor