code: def get_periods(start_dt, end_dt, freq):
      """
      The number of periods in the specified range.
  
      Parameters
      ----------
      start_dt: datetime
      end_dt: datetime
      freq: str
  
      Returns
      -------
      int
  
      """
      return len(
          get_periods_range(start_dt=start_dt, end_dt=end_dt, freq=freq)
      )
  
file_path: catalyst/catalyst/exchange/utils/datetime_utils.py
imports: import calendar
  import math
  import re
  from datetime import datetime, timedelta, date
  import pandas
  import pytz
  from catalyst.exchange.exchange_errors import InvalidHistoryFrequencyError, InvalidHistoryFrequencyAlias
label_desc: Use image node_id 5 for calling a global function with example usage: get_periods(start_dt, end_dt, freq) and returns: len