code: def lines_generator(self):
      for num, (index, line) in enumerate(self._data.iterrows()):
          if self._group_feature_num is None:
              yield num, series_to_line(line, self._sep) + "\n"
          else:
              yield line.iloc[self._group_feature_num], series_to_line(
                  line, self._sep
              ) + "\n"
  
file_path: catboost/catboost/python-package/catboost/eval/_readers.py
imports: import pandas
  from .utils import series_to_line
label_desc: Use image node_id 2 for calling the _SimpleDataReader obj's underlying member method code with example usage: obj.lines_generator() without return types