日期不会出现在情节中（使用matplotlib）

Question

我想绘制以下数据

>>> AllSummary
      upload_date  Gross Loan Amount  NewPerfColumn
    0  2018-02-19       1.532472e+11   2.624765e+08
    1  2018-03-01       1.475863e+11   1.361267e+08
    2  2018-03-12       1.376221e+11   1.133450e+08

如下所示，列＆＃34; upload_date＆＃34;肯定被认为是一个日期

AllSummary.dtypes
upload_date          datetime64[ns]
Gross Loan Amount           float64
NewPerfColumn               float64
dtype: object

但是当我绘制数据时，它显示x-xis为数字（而不是日期）：代码在下面

x=AllSummary['upload_date']
y1 =AllSummary['Gross Loan Amount']
y2 =AllSummary['NewPerfColumn']
fig, ax1 = plt.subplots()

ax2 = ax1.twinx()
ax1.plot(x, y1, 'g-')
ax2.plot(x, y2, 'b-')

ax1.set_xlabel('Date')
ax1.set_ylabel('Gross Loan Amount', color='g')
ax2.set_ylabel('Performance', color='b')

plt.show()

为什么会这样？