title: Graphviz's executable not found
body: <p>I'm trying to learn data science online and when I run a script from one of a Google video, I get this error:</p>
  
  <pre><code>File "/documents/testpython.py", line 547, in &lt;module&gt;
  graph.write_pdf("iris pdf")
  
  File "/anaconda/lib/python3.5/site-packages/pydotplus/graphviz.py", line 1810, in &lt;lambda&gt;
  prog=self.prog: self.write(path, format=f, prog=prog)
  
  File "/anaconda/lib/python3.5/site-packages/pydotplus/graphviz.py", line 1918, in write
  fobj.write(self.create(prog, format))
  
  File "/anaconda/lib/python3.5/site-packages/pydotplus/graphviz.py", line 1960, in create
  'GraphViz\'s executables not found')
  
  pydotplus.graphviz.InvocationException: GraphViz's executables not found
  </code></pre>
  
  <p><strong>Here is the script:</strong></p>
  
  <pre><code>from sklearn.datasets import load_iris
  import numpy as np
  from sklearn import tree
  
  iris = load_iris()
  test_idx = [0,50,100]
  
  train_target = np.delete(iris.target, test_idx)
  train_data = np.delete(iris.data, test_idx, axis = 0)
  
  test_target = iris.target[test_idx]
  test_data = iris.data[test_idx]
  
  clf = tree.DecisionTreeClassifier()
  clf.fit(train_data, train_target)
  
  from sklearn.externals.six import StringIO
  import pydotplus
  
  dot_data = StringIO()
  tree.export_graphviz(clf, out_file=dot_data, feature_names=iris.feature_names, class_names=iris.target_names, filled=True, rounded=True, impurity=False)
  graph = pydotplus.graph_from_dot_data(dot_data.getvalue())
  graph.write_pdf("iris pdf")
  </code></pre>
  
  <p>If anyone has any idea, I'm not sure if the problem comes from my version of python or the libraries or anything else...</p>
  
  <p>Thanks</p>