input: 
  from typing import List
  
  def predict_temperature(temperature_list: List[float], alpha: float = 0.5) -> float:
      """Uses the exponential smoothing algorithm to predict the next day's forecast temperature 
      given the past three day's forecast temperatures.
      >>> predict_temperature([21, 22, 20])
      21.0
      >>> predict_temperature([15, 17, 16])
      16.5
      """
      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:     predicted_temperature = temperature_list[-1]  # Initializing prediction
      for temperature in temperature_list[:-1]:
          predicted_temperature = alpha * temperature + (1 - alpha) * predicted_temperature
      return predicted_temperature