code: def _get_date(
      self,
      file_or_df: [Path, pd.DataFrame],
      *,
      is_begin_end: bool = False,
      as_set: bool = False,
  ) -> Iterable[pd.Timestamp]:
      if not isinstance(file_or_df, pd.DataFrame):
          df = self._get_source_data(file_or_df)
      else:
          df = file_or_df
      if df.empty or self.date_field_name not in df.columns.tolist():
          _calendars = pd.Series(dtype=np.float32)
      else:
          _calendars = df[self.date_field_name]
  
      if is_begin_end and as_set:
          return (_calendars.min(), _calendars.max()), set(_calendars)
      elif is_begin_end:
          return _calendars.min(), _calendars.max()
      elif as_set:
          return set(_calendars)
      else:
          return _calendars.tolist()
  
imports: import abc
  import shutil
  import traceback
  from pathlib import Path
  from typing import Iterable, List, Union
  from functools import partial
  from concurrent.futures import ThreadPoolExecutor, as_completed, ProcessPoolExecutor
  import fire
  import numpy
  import pandas
  from tqdm import tqdm
  from loguru import logger
  from qlib.utils import fname_to_code, code_to_fname
label_desc: Use image node_id 4 for calling the DumpDataBase obj's underlying member method code with example usage: obj._get_date(file_or_df) and returns: _calendars,  _calendars,  set, _calendars,  _calendars, set, _calendars