当我在visualize决策树，运行以下代码时，报错: InvocationException: GraphViz‘s executables not found

import pydotplusfrom io import StringIOdot_data = http://www.mamicode.com/StringIO()>
查阅资料后发现,原来我没有安装GraphViz‘s executables.我是用pip安装的Graphviz,但是Graphviz不是一个python tool，你仍然需要安装GraphViz‘s executables.
problem solved:
You need to install the GraphViz package <http://www.graphviz.org/> so that graph.dag can invoke dot.
安装完之后，再运行还是报错：Exception: "dot.exe" not found in path.
那是因为你没有将GraphViz安装目录的bin目录放到环境变量的path路径中，dot.exe在那个目录下。
Note: As of version 2.31, the Visual Studio package no longer alters the PATH variable or accesses the registry at all. If you wish to use the command-line interface to Graphviz or are using some other program that calls a Graphviz program, you will need to set the PATH variable yourself.
设置完如果还是报同样的错误，你需要重启pyhon IDE.
REF.
[1]http://stackoverflow.com/questions/27666846/pydot-invocationexception-graphvizs-executables-not-found
[2]http://markmail.org/message/coebrty3itq426c2
[3]http://stackoverflow.com/questions/18438997/why-is-pydot-unable-to-find-graphvizs-executables-in-windows-8
[4]http://www.graphviz.org/Download_windows.php
InvocationException: GraphViz's executables not found