python - Is it possible to print the decision tree in scikit-learn?

Question

Is there a way to print a trained decision tree in scikit-learn? I want to train a decision tree for my thesis and I want to put the picture of the tree in the thesis. Is that possible?

Answer 1

There is a method to export to graph_viz format: http://scikit-learn.org/stable/modules/generated/sklearn.tree.export_graphviz.html

So from the online docs:

>>> from sklearn.datasets import load_iris
>>> from sklearn import tree
>>>
>>> clf = tree.DecisionTreeClassifier()
>>> iris = load_iris()
>>>
>>> clf = clf.fit(iris.data, iris.target)
>>> tree.export_graphviz(clf,
...     out_file='tree.dot')    

Then you can load this using graph viz, or if you have pydot installed then you can do this more directly: http://scikit-learn.org/stable/modules/tree.html

>>> from sklearn.externals.six import StringIO  
>>> import pydot 
>>> dot_data = StringIO() 
>>> tree.export_graphviz(clf, out_file=dot_data) 
>>> graph = pydot.graph_from_dot_data(dot_data.getvalue()) 
>>> graph.write_pdf("iris.pdf") 

Will produce an svg, can't display it here so you'll have to follow the link: http://scikit-learn.org/stable/_images/iris.svg

Update

It seems that there has been a change in the behaviour since I first answered this question and it now returns a list and hence you get this error:

AttributeError: 'list' object has no attribute 'write_pdf'

Firstly when you see this it's worth just printing the object and inspecting the object, and most likely what you want is the first object:

graph[0].write_pdf("iris.pdf")

Thanks to @NickBraunagel for the comment