class_docstr: FoldFile is the realisation of the interface of FoldStorage. It always saves data to file before reset them.
  All files place to the special directory 'folds'.
class_docstr_tok: ["FoldFile","is","the","realisation","of","the","interface","of","FoldStorage",".","It","always","saves","data","to","file","before","reset","them",".","All","files","place","to","the","special","directory","'folds","'","."]
code: def __init__(self, fold, storage_name, sep, column_description):
      super(_FoldFile, self).__init__(
          fold,
          storage_name,
          sep=sep,
          column_description=column_description,
      )
      self._file_path = os.path.join(self.default_dir, storage_name)
      self._prepare_path()
      self._lines = []
      self._file = None
  
imports: from __future__ import print_function
  import os
  from ..None import CatBoostError
  from ..eval.log_config import get_eval_logger
  from .utils import make_dirs_if_not_exists
label_desc: Use image node_id 1 to create a new _FoldFile object from inherited base classes: FoldStorage with example: obj = _FoldFile(fold, storage_name, sep, column_description)