当我打开cmd并键入

python
import _graphviz

_graphviz可以导入，但是当我运行一个调用。py文件，这里面有一行。py文件是什么

import pygraphviz as pgv

然后它将无法导入_graphviz，它显示以下信息：

Traceback (most recent call last):
  File "E:\project\graph\analysis\x64\Debug\gengraph.py", line 1, in <module>
    import pygraphviz as pgv
  File "C:\Program Files\Python27\lib\site-packages\pygraphviz\__init__.py", lin
e 54, in <module>
    from agraph import AGraph, Node, Edge, Attribute, ItemAttribute
  File "C:\Program Files\Python27\lib\site-packages\pygraphviz\agraph.py", line
20, in <module>
    import graphviz as gv
  File "C:\Program Files\Python27\lib\site-packages\pygraphviz\graphviz.py", lin
e 7, in <module>
    import _graphviz
ImportError: No module named _graphviz

能不能帮帮我，欢迎指教，谢谢！