class_docstr: Manager for trading calendar
      - BaseStrategy and BaseExecutor will use it
code: def get_freq(self) -> str:
      return self.freq
  
imports: from __future__ import annotations
  from abc import abstractmethod
  from typing import Any, Set, Tuple, TYPE_CHECKING, Union
  import numpy
  from qlib.utils.time import epsilon_change
  import warnings
  import pandas
  from ..data.data import Cal
label_desc: Use image node_id 5 for calling the TradeCalendarManager obj's underlying member method code with example usage: obj.get_freq() and returns: self