我一直在尝试向绘图添加一个附加轴，但是我一直收到错误消息：“要解压缩的值太多（预期2）”。我像the documentation says那样做-传递函数的元组。这是代码：
def forward(ignored):
return climate_change.index
def inverse(ignored):
return np.flip(climate_change.index)
fig, ax = plt.subplots()
ax.scatter(climate_change['co2'], climate_change['relative_temp'], c=climate_change.index)
ax.set_xlabel('CO2 [ppm]')
ax.set_ylabel('Relative temperature [°C]')
# Throws "too many values to unpack (expected 2)"
secax = ax.secondary_xaxis('top', functions=(forward, inverse))
secax.set_xlabel('Time [year]')
plt.show()