docs: def rate_of_return(period_ret, base_period):
      """
      Convert returns to 'one_period_len' rate of returns: that is the value the
      returns would have every 'one_period_len' if they had grown at a steady
      rate
  
      Parameters
      ----------
      period_ret: pd.DataFrame
          DataFrame containing returns values with column headings representing
          the return period.
      base_period: string
          The base period length used in the conversion
          It must follow pandas.Timedelta constructor format (e.g. '1 days',
          '1D', '30m', '3h', '1D1h', etc)
  
      Returns
      -------
      pd.DataFrame
          DataFrame in same format as input but with 'one_period_len' rate of
          returns values.
      """
      period_len = period_ret.name
      conversion_factor = (pd.Timedelta(base_period) /
                           pd.Timedelta(period_len))
      return period_ret.add(1).pow(conversion_factor).sub(1)