input: 
  def predict_temperature(temperature_list):
      """
      This function uses the exponential smoothing algorithm to predict the 
      next day's forecasted temperature given the past three day's forecasted 
      temperatures.
  
      >>> predict_temperature([21, 22, 20])
      21.0
      """
      alpha = 0.5  # Confidence value
      predicted_temperature = temperature_list[-1]  # Initializing prediction
      for temperature in temperature_list[:-1]:
          predicted_temperature = alpha * temperature + (1 - alpha) * predicted_temperature
      return predicted_temperature
  
output:     alpha = 0.5  # Confidence value
      predicted_temperature = temperature_list[-1]  # Initializing prediction
      for temperature in temperature_list[:-1]:
          predicted_temperature = alpha * temperature + (1 - alpha) * predicted_temperature
      return predicted_temperature