code: def to_excess_returns(returns, rf, nperiods=None):
      
      if type(rf) is float and nperiods is not None:
          _rf = deannualize(rf, nperiods)
      else:
          _rf = rf
  
      return returns - _rf
docs: Given a series of returns, it will return the excess returns over rf.
  
      Args:
          * returns (Series, DataFrame): Returns
          * rf (float, Series): `Risk-Free rate(s) <https://www.investopedia.com/terms/r/risk-freerate.asp>`_ expressed in annualized term or return series
          * nperiods (int): Optional. If provided, will convert rf to different
              frequency using deannualize only if rf is a float
      Returns:
          * excess_returns (Series, DataFrame): Returns - rf