code: def future_value(present_value, annual_rate, periods_per_year, years):
      
  
      # The nominal interest rate per period (rate) is how much interest you earn during a
      # particular length of time, before accounting for compounding. This is typically
      # expressed as a percentage.
      rate_per_period = annual_rate / float(periods_per_year)
  
      # How many periods in the future the calculation is for.
      periods = periods_per_year * years
  
      return present_value * (1 + rate_per_period) ** periods
docs: Calculates the future value of money invested at an anual interest rate,
      x times per year, for a given number of years.
  
      Args:
          present_value: int or float, the current value of the money (principal).
  
          annual_rate: float 0 to 1 e.g., .5 = 50%), the interest rate paid out.
  
          periods_per_year: int, the number of times money is invested per year.
  
          years: int, the number of years invested.
  
      Returns:
          Float, the future value of the money invested with compound interest.