升级python2至python3解决依赖关系

1.最小化安装centos7，在升级python3的时候会出现很多包未安装，为解决依赖关系：

yum -y install gcc gcc-c++ zlib zlib-devel libffi-devel deltarpm kernel-devel kernel-headers make
yum -y install bzip2 bzip2-devel openssl-devel ncurses-devel sqlite-devel readline-devel tk-devel gdbm-devel db4-devel libpcap-devel
yum -y install xz-devel
为什么要分三步？因为在安装过程中一次性安装的时候，我的服务器出现了这个报错：
zvbi-fonts-0.2.35-1.el6.noarch: [Errno 256] No more mirrors to try
分开一步步安装则不报错了

wget https://www.python.org/ftp/python/3.6.1/Python-3.6.1.tgz
tar xf Python-3.6.1.tgz
cd Python-3.6.1/
./configure --prefix=/usr/local/python/python3
make
make install
mv /usr/bin/python /usr/bin/python.bak
ln -s /usr/local/python/python3/bin/python3 /usr/bin/python
ln -s /usr/local/python/python3/bin/pip3 /usr/bin/pip
vi /usr/bin/yum
vi /usr/libexec/urlgrabber-ext-down
修改/usr/bin/yum和/usr/libexec/urlgrabber-ext-down，将 #!/usr/bin/python 改为 #!/usr/bin/python2.7

2. 这样升级出来的Python3就自动安装了setuptools和pip：

pip的位置是在/usr/local/python/python3/bin/目录下，并不在/usr/local/python/python3/lib/python3.5/site-packages/下，找了十分钟才找到解决办法。

[root@www bin]# pip -V
pip 9.0.1 from /usr/local/python/python3/lib/python3.6/site-packages (python 3.6)