title: Pandas.plotting doesn't show graph
body: <p>I'm following the tutorial in the book "introduction to machine learning with python" and i've copied the following code:</p>
  
  <pre><code>#create dataframe from data in X_train
  #label the colums using the strings in iris_dataset.features_names
  iris_dataframe = pd.DataFrame(X_train, columns = iris_dataset.feature_names)
  #create a scatter matrix from the dataframe, color by y_train
  pd.plotting.scatter_matrix(iris_dataframe,c=y_train,
                             figsize=(15,15), marker='o', 
                             hist_kwds={'bins':20},s=60, 
                             alpha=.8,
                             cmap=mglearn.cm3)
  </code></pre>
  
  <p>It should plot a graph,but it only print those lines:</p>
  
  <pre><code>array([[&lt;matplotlib.axes._subplots.AxesSubplot object at 0x7f0d073934a8&gt;,
          &lt;matplotlib.axes._subplots.AxesSubplot object at 0x7f0d07352908&gt;,
          &lt;matplotlib.axes._subplots.AxesSubplot object at 0x7f0d07376e48&gt;,
          &lt;matplotlib.axes._subplots.AxesSubplot object at 0x7f0d0732ee48&gt;],
         [&lt;matplotlib.axes._subplots.AxesSubplot object at 0x7f0d072e3f28&gt;,
          &lt;matplotlib.axes._subplots.AxesSubplot object at 0x7f0d072e3f60&gt;,
          &lt;matplotlib.axes._subplots.AxesSubplot object at 0x7f0d07308ac8&gt;,
          &lt;matplotlib.axes._subplots.AxesSubplot object at 0x7f0d07211400&gt;],
         [&lt;matplotlib.axes._subplots.AxesSubplot object at 0x7f0d071ca470&gt;,
          &lt;matplotlib.axes._subplots.AxesSubplot object at 0x7f0d07183470&gt;,
          &lt;matplotlib.axes._subplots.AxesSubplot object at 0x7f0d071be470&gt;,
          &lt;matplotlib.axes._subplots.AxesSubplot object at 0x7f0d07165e80&gt;],
         [&lt;matplotlib.axes._subplots.AxesSubplot object at 0x7f0d07127390&gt;,
          &lt;matplotlib.axes._subplots.AxesSubplot object at 0x7f0d070e5390&gt;,
          &lt;matplotlib.axes._subplots.AxesSubplot object at 0x7f0d0709d390&gt;,
          &lt;matplotlib.axes._subplots.AxesSubplot object at 0x7f0d07047da0&gt;]], dtype=object)
  </code></pre>
  
  <p>Can someone tell me a reason?</p>
  
  <p>EDIT-SOLVED:I do not know why but a after a re-run of the cells, the graph apperead..</p>