CentOS 7 默认的Python版本是python2.7.5。因为yum依赖于默认的python版本的缘由，所以要先保留默认版本，并修改yum文件头部后，才能开始安装更新python2和python3两个最新版本。（python2和python3共存）
一. 保留默认python版本2.7.5，并修改yum头部，保持yum对默认版本python2.7.5的依赖
1.su root # 获取root权限
2.mv /usr/bin/python2.7 /usr/bin/python2.7.5 # 保留默认版本python为python2.7.5
ln -s /usr/bin/python2.7.5 /usr/local/bin/python2.7.5 # 创建软连接
3.ll /usr/bin/yum* # 查看/usr/bin/目录下所有yum文件（7个）头部
4.vi /usr/bin/yum* # 修改/usr/bin/目录下所有yum文件（7个）头部
#!/usr/bin/python —> #!/usr/bin/python2.7.5
5.vi /usr/libexec/urlgrabber-ext-down # 修改/usr/libexec/目录下 urlgrabber-ext-down头部
#!/usr/bin/python —> #!/usr/bin/python2.7.5
二. 安装最新版python2.7.13和python3.6.2（python2和python3共存，修改后默认版本为python3.6.2）
准备工作：
1. 安装wget命令（可以在线下载安装包的命令）
yum -y install wget
2. 准备编译环境
yum groupinstall 'Development Tools'
yum install zlib-devel bzip2-devel openssl-devel ncurses-devel
3. 下载并安装最新版本的python2和python3的tgz压缩文件
https://www.python.org/ftp/python/2.7.13/Python-2.7.13.tgz
https://www.python.org/ftp/python/3.6.2/Python-3.6.2.tgz
开始安装：
1. 进入下载目录：
cd /usr/local/src
2. 下载并安装最新版本python2：
wget https://www.python.org/ftp/python/2.7.13/Python-2.7.13.tgz
tar zxvf Python-2.7.13.tgz
cd Python-2.7.13
./configure
make all
make install
make clean
make distclean
rm -rf /usr/bin/python
rm -rf /usr/bin/python2
rm -rf /usr/bin/python2.7
ln -s /usr/local/bin/python2.7 /usr/bin/python
ln -s /usr/local/bin/python2.7 /usr/bin/python2
ln -s /usr/local/bin/python2.7 /usr/bin/python2.7
/usr/bin/python -V
/usr/bin/python2 -V
/usr/bin/python2.7 -V
rm -rf /usr/local/bin/python
rm -rf /usr/local/bin/python2
ln -s /usr/local/bin/python2.7 /usr/local/bin/python
ln -s /usr/local/bin/python2.7 /usr/local/bin/python2
python -V
python2 -V
python2.7 -V
3. 下载并安装最新版本python3：
wget https://www.python.org/ftp/python/3.6.2/Python-3.6.2.tgz
tar zxvf Python-3.6.2.tgz
cd Python-3.6.2
./configure
make all
make install
make clean
make distclean
rm -rf /usr/bin/python
rm -rf /usr/bin/python3
rm -rf /usr/bin/python3.6
ln -s /usr/local/bin/python3.6 /usr/bin/python
ln -s /usr/local/bin/python3.6 /usr/bin/python3
ln -s /usr/local/bin/python3.6 /usr/bin/python3.6
/usr/bin/python -V
/usr/bin/python3 -V
/usr/bin/python3.6 -V
rm -rf /usr/local/bin/python
rm -rf /usr/local/bin/python3
ln -s /usr/local/bin/python3.6 /usr/local/bin/python
ln -s /usr/local/bin/python3.6 /usr/local/bin/python3
python -V
python3 -V
python3.6 -V