报错如下：

graphviz.backend.ExecutableNotFound: failed to execute 'dot', make sure the Graphviz executables are on your systems' PATH

大家习惯pip install graphviz去安装，但是graphviz是个软件，不能单独用Pip安装。

1、下载安装

Graphviz的官网下载：Download | Graphviz，下载后按照提示进行安装就可以了；

2、然后在pip安装

pip install graphviz

3、如果没有添加环境变量，自己手动添加。添加在系统环境变量里

路径是自己的安装路径

D:\python\graphviz\bin
D:\python\graphviz\bin\dot.exe # 如果只添加第一个没用，就在加他

目前，已经安装好了。但是在运行python还是会报错。我们在python开头代码里还需要加以下代码

import os
os.environ["PATH"] += os.pathsep + r'D:\Graphviz\bin/'

示例代码：

from sklearn import tree
from sklearn.model_selection import train_test_split
from sklearn import datasets

import os
os.environ["PATH"] += os.pathsep + r'D:\Graphviz\bin/'

iris = datasets.load_iris()
X = iris.data
y = iris.target

X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.8)
clf=tree.DecisionTreeClassifier(criterion='gini')
clf=clf.fit(X_train,y_train)
score=clf.score(X_test,y_test)
print(score)

import graphviz
feature_names=['a','b','c',"d"]

class_names=['d','dd','ddd',"dddd"]
tree_data=tree.export_graphviz(clf,
                               feature_names=feature_names,
                               class_names=class_names,
                               filled=True,
                               rounded=True
                               )
graph=graphviz.Source(tree_data)
graph.view()