code: def get_symbol_rets(symbol, start=None, end=None):
      
  
      return SETTINGS['returns_func'](symbol,
                                      start=start,
                                      end=end)
docs: Calls the currently registered 'returns_func'
  
      Parameters
      ----------
      symbol : object
          An identifier for the asset whose return
          series is desired.
          e.g. ticker symbol or database ID
      start : date, optional
          Earliest date to fetch data for.
          Defaults to earliest date available.
      end : date, optional
          Latest date to fetch data for.
          Defaults to latest date available.
  
      Returns
      -------
      pandas.Series
          Returned by the current 'returns_func'