code: def period_break(dates, period):
      
      current = getattr(dates, period)
      previous = getattr(dates - 1 * dates.freq, period)
      return np.nonzero(current - previous)[0]
docs: Returns the indices where the given period changes.
  
      Parameters
      ----------
      dates : PeriodIndex
          Array of intervals to monitor.
      period : string
          Name of the period to monitor.