input: Write a function to predict the next day's forecast temperature using the exponential smoothing algorithm given the past three day's forecast temperatures. If the list is empty, return None.
  def predict_temperature(temperature_list):
      if not temperature_list:
          return None
      alpha = 0.5
      predicted_temperature = temperature_list[-1]
      for temperature in temperature_list[:-1]:
          predicted_temperature = alpha*temperature + (1-alpha)*predicted_temperature
      return predicted_temperature
  assert predict_temperature([21, 22, 20])==21
  assert predict_temperature([15, 18, 20])==17
  assert predict_temperature([10, 12, 11])==11.5
  assert predict_temperature([25, 26, 24])==24.5
  assert predict_temperature([])==None
output: def predict_temperature(temperature_list):
      if not temperature_list:
          return None
      alpha = 0.5
      predicted_temperature = temperature_list[-1]
      for temperature in temperature_list[:-1]:
          predicted_temperature = alpha*temperature + (1-alpha)*predicted_temperature
      return predicted_temperature