graphviz已经下载好，并写入环境变量中，而且也已经输入pip install graphviz ,pip install pydot ,仍然报错：
`pydot` failed to call GraphViz.Please install GraphViz (https://www.graphvi.org)...
修正方法：不要用pip install graphviz 用conda install graphviz即可解决
#在anaconda prompt中依次输入：
pip uninstall graphviz
conda install graphviz
