class_docstr: Base Evaluation class.
docstr: Message at start of preprocessing
docstr_tok: ["Message","at","start","of","preprocessing"]
code: def _print_prep_start(self):
      """Message at start of preprocessing"""
      return "Preprocessing"
  
imports: from __future__ import division, with_statement
  import warnings
  import numpy
  from ._base_functions import parse_key, set_job, cat, check_scorer, make_learners, make_tansformers, check_instances
  from ..index import FoldIndex
  from ..parallel import ParallelEvaluation
  from ..parallel.base import BaseBackend, IndexMixin
  from ..metrics import Data, assemble_data
  from ..utils.formatting import _flatten, _check_instances
  from ..utils import print_time, safe_print, assert_correct_format
  from ..externals.joblib import delayed
  from ..externals.sklearn.base import clone
label_desc: Use image node_id 8 for calling the BaseEval obj's underlying member method code with example usage: obj._print_prep_start() and returns: str