问题二：pip install python-igraph 报错，C core of igraph 没有安装。

（一）问题描述

        Centos7 安装python-igraph时，pip install python-igraph 报错，C core of igraph 没有安装。

failure: repodata/repomd.xml from base: [Errno 256] No more mirrors to try.
Cannot find the C core of igraph on this system using pkg-config.
We will now try to download and compile the C core from scratch.
Version number of the C core: 0.7.1.post6
We will also try: 0.7.1

Version 0.7.1.post6 of the C core of igraph is not found among the nightly builds.

Use the --c-core-version switch to try a different version.
Could not download and compile the C core of igraph.

（二）解决办法

        网上的方法都试过，搞了好几天，焦头烂额，也没有整出来。最后看了源码。才知道它安装的时候，会下载igraph。也就是C core。具体解决方法：

     1. 下载：igraph-0.7.1.tar

     2. 解压：tar -zxvf igraph-0.7.1.tar.gz

     3.安装：

./configure 

make

make install

   4. 在安装pip install python-igraph，命令如下：

pip install -v python-igraph --install-option="--c-core-url=【igraph路径】/igraph-0.7.1.tar.gz"

pip install -v python-igraph --install-option="--c-core-url=http://127.0.0.1/imagedeps/igraph-0.7.1.tar.gz"