code: def mean_historical_return(prices, frequency=252):
      
      if not isinstance(prices, pd.DataFrame):
          warnings.warn("prices are not in a dataframe", RuntimeWarning)
          prices = pd.DataFrame(prices)
      daily_returns = daily_price_returns(prices)
      return daily_returns.mean() * frequency
docs: Calculate annualised mean (daily) historical return from input (daily) asset prices.
  
      :param prices: adjusted closing prices of the asset, each row is a date
                     and each column is a ticker/id.
      :type prices: pd.DataFrame
      :param frequency: number of time periods in a year, defaults to 252 (the number
                        of trading days in a year)
      :type frequency: int, optional
      :return: annualised mean (daily) return for each asset
      :rtype: pd.Series