問題二：pip install python-igraph 報錯，C core of igraph 沒有安裝。

（一）問題描述

        Centos7 安裝python-igraph時，pip install python-igraph 報錯，C core of igraph 沒有安裝。

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）解決辦法

        網上的方法都試過，搞了好幾天，焦頭爛額，也沒有整出來。最后看了源碼。才知道它安裝的時候，會下載igraph。也就是C core。具體解決方法：

     1. 下載：igraph-0.7.1.tar

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

     3.安裝：

./configure 

make

make install

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

pip install -v python-igraph --install-option="--c-core-url=【igraph路徑】/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"