title: No module named _graphviz
body: <p>I installed graphviz and pygraphviz, when I open a cmd and type</p>
  
  <pre><code>python
  import _graphviz
  </code></pre>
  
  <p>_graphviz can be imported, but when I run a C++ program which will invoke a .py file, there is a line in this .py file which is</p>
  
  <pre><code>import pygraphviz as pgv
  </code></pre>
  
  <p>Then it will not be able to import _graphviz, it shows the following info:</p>
  
  <pre><code>Traceback (most recent call last):
    File "E:\project\graph\analysis\x64\Debug\gengraph.py", line 1, in &lt;module&gt;
      import pygraphviz as pgv
    File "C:\Program Files\Python27\lib\site-packages\pygraphviz\__init__.py", lin
  e 54, in &lt;module&gt;
      from agraph import AGraph, Node, Edge, Attribute, ItemAttribute
    File "C:\Program Files\Python27\lib\site-packages\pygraphviz\agraph.py", line
  20, in &lt;module&gt;
      import graphviz as gv
    File "C:\Program Files\Python27\lib\site-packages\pygraphviz\graphviz.py", lin
  e 7, in &lt;module&gt;
      import _graphviz
  ImportError: No module named _graphviz
  </code></pre>
  
  <p>Can you help me, any advice is welcome, thank you!</p>