一般来说，virtualenv中只能用pip instal 来安装三方库
但是有的三方库只能用apt-get install 来安装
相关经验：
2020年8月9日
https://stackoverflow.com/questions/15661384/python-does-not-see-pygraphviz
这个是关于import gv出错的问题
开始发现 pip install pygraphviz 无法安装，sudo pip 也不行
后来这个帖子里面指出，执行以下就行，理由是这是pygraphviz自身的问题，呵呵
sudo apt-get install -y graphviz libgraphviz-dev pkg-config python-pip
sudo pip install pygraphviz
2020年8月9日
另外，https://askubuntu.com/questions/581648/install-package-into-virtualenv-using-apt-get
这个帖子里面说：
Another alternative is to download the file with apt-get download, extract it with dpkg -x and to move the extracted files to your virtualenv:
Example:
apt-get download python-xyz
assume this results in:
./python-xyz_1.2.3-3ubuntu5_amd64.deb
Then, use dpkg to extract the data portion of the .deb file:
dpkg -x python-xyz_1.2.3-3ubuntu5_amd64.deb ./xyz-tmp
In the newly created ./xyz-tmp directory, you now have all files that would have been installed to / (root) had you used apt-get install.
Assume they are:
./xyz-tmp/usr/lib/python2.7/dist-packages/xyz/
./xyz-tmp/usr/lib/python2.7/dist-packages/xyz-1.2.3.egg-info
You still need to map the subdirectories (e.g. dist-packages vs. site-packages), and can then move the files into your virtualenv (assuming a virtualenv /home/user/.virtualenvs/py27):
mv ./xyz-tmp/usr/lib/python2.7/dist-packages/* /home/user/.virtualenvs/py27/lib/python2.7/site-packages/
Compared to my previous answer, this approach has the advantage that you don't have to research which files got installed, because you can see them in the extraction directory. It still requires a mapping of directories between the extracted archive and the virtualenv.
