docstr: get limit type
docstr_tok: ["get","limit","type"]
code: def _get_limit_type(
      self, limit_threshold: Union[tuple, float, None]
  ) -> str:
      """get limit type"""
      if isinstance(limit_threshold, tuple):
          return self.LT_TP_EXP
      elif isinstance(limit_threshold, float):
          return self.LT_FLT
      elif limit_threshold is None:
          return self.LT_NONE
      else:
          raise NotImplementedError(
              f"This type of `limit_threshold` is not supported"
          )
  
imports: from __future__ import annotations
  from collections import defaultdict
  from typing import TYPE_CHECKING, Any, Dict, List, Optional, Tuple, Type, Union, cast
  from ..utils.index_data import IndexData
  import random
  import numpy
  import pandas
  from qlib.backtest.position import BasePosition
  from ..config import C
  from ..constant import REG_CN, REG_TW
  from ..data.data import D
  from ..log import get_module_logger
  from .decision import Order, OrderDir, OrderHelper
  from .high_performance_ds import BaseQuote, NumpyQuote
label_desc: Use image node_id 3 for calling the Exchange obj's underlying member method code with example usage: obj._get_limit_type(limit_threshold) and returns: self, self, self