centos已经安装了python2，同时安装python3

安装相关软件包：

yum install zlib-devel bzip2-devel openssl-devel ncurses-devel sqlite-devel readline-devel tk-devel gcc make

安装python3：

wget https://www.python.org/ftp/python/3.7.5/Python-3.7.5.tar.xz

 解压：

tar -xvJf Python-3.7.5.tar.xz 

进入解压后的目录：

cd Python-3.7.5

编译安装

./configure prefix=/usr/local/Python-3.7.5

make && make install

安装完毕，/usr/local/目录下就会有Python-3.7.5了

因此我们可以添加软链到执行目录下/usr/bin

ln -s /usr/local/Python-3.7.5/bin/python3  /usr/bin/python3

输入python3 --version提示Python 3.7.5代表安装成功了

 安装了python3,  pip3去哪里了？

pip3就在Python-3.7.5的bin目录里面/usr/local/Python-3.7.5/bin/

添加软链：

ln -s /usr/local/Python-3.7.5/bin/pip3 /usr/bin/pip3

可以看到/usr/bin下面可以看到创建了pip3的软链

运行pip3 --version

py_version=`python -V 2>&1|awk -F' ' '{print $2}'|awk -F'.' '{print $1}'`
if [ $py_version -eq 2 ]
then
    #安装python3
    yum install zlib-devel bzip2-devel openssl-devel ncurses-devel sqlite-devel readline-devel tk-devel gcc make libffi-devel 
    wget https://www.python.org/ftp/python/3.7.5/Python-3.7.5.tar.xz
    tar -xvJf Python-3.7.5.tar.xz 
    cd Python-3.7.5
    ./configure prefix=/usr/local/Python-3.7.5
    make&&make install
    py_run_dir=`which python|awk -F"python" '{print$1}'`
    ln -s /usr/local/Python-3.7.5/bin/python3  ${py_run_dir}python3
    py_version=`python3 -V 2>&1|awk -F' ' '{print $2}'|awk -F'.' '{print $1}'`
    if [ $py_version -eq 3 ]
    then
        echo `python3 -V 2>&1`" install success"
    fi
    #软链pip3
    ln -s /usr/local/Python-3.7.5/bin/pip3  ${py_run_dir}pip3
fi