code: def lines_generator(self):
      with open(self._file_name, "r") as file:
          if self._has_header:
              file.readline()
          for num, line in enumerate(file):
              if self._group_feature_num is None:
                  group_id = num
              else:
                  features = line.strip().split(
                      self._sep, self._group_feature_num + 1
                  )
                  group_id = features[self._group_feature_num]
              yield int(float(group_id)), line
  
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 _SimpleStreamingFileReader obj's underlying member method code with example usage: obj.lines_generator() without return types