code: def _maybe_cache(arg, format, cache, convert_listlike):
      
      from pandas import Series
      cache_array = Series()
      if cache:
          # Perform a quicker unique check
          from pandas import Index
          unique_dates = Index(arg).unique()
          if len(unique_dates) < len(arg):
              cache_dates = convert_listlike(unique_dates.to_numpy(),
                                             True, format)
              cache_array = Series(cache_dates, index=unique_dates)
      return cache_array
docs: Create a cache of unique dates from an array of dates
  
      Parameters
      ----------
      arg : integer, float, string, datetime, list, tuple, 1-d array, Series
      format : string
          Strftime format to parse time
      cache : boolean
          True attempts to create a cache of converted values
      convert_listlike : function
          Conversion function to apply on dates
  
      Returns
      -------
      cache_array : Series
          Cache of converted, unique dates. Can be empty