title: when using matplotlib, AttributeError: 'numpy.datetime64' object has no attribute 'toordinal'
body: <p>I just plot the sp500 data using matplotlib, and I got an error of</p>
  <blockquote>
  <p>AttributeError: 'numpy.datetime64' object has no attribute
  'toordinal'.</p>
  </blockquote>
  <p>I googled for a long time and I didn't find a solution. Can somebody help me? thanks</p>
  <pre><code>    plt.plot(SP500_df['Date'], 
           SP500_df['Adj Close'], label=SYMBOL, color='green')
  </code></pre>
  <p>I did print(SP500_df.info()) and it does show the date column is a type of datetime64.</p>
  <pre><code> #   Column     Non-Null Count  Dtype
  ---  ------     --------------  -----
   0   Date       83 non-null     datetime64[ns]
   1   Adj Close  83 non-null     float64
  </code></pre>
  <p>I am using python 3.6 and before showing the above error, there was a warning  of</p>
  <p>C:\Python36\lib\site-packages\matplotlib\axes_base.py:248: FutureWarning: Support for multi-dimensional indexing (e.g. <code>obj[:, None]</code>) is deprecated and will be removed in a future version.  Convert to a numpy array before indexing instead</p>
  <p>I googled for a long time and I didn't find a solution. Can somebody help me? thanks</p>