系统为Centos7.8，默认已经安装了Python2.7.5。
Python3和Python2可以共存，安装Python3不要卸载Python2，因为yum依赖于Python2。
刚开始不清楚，按照网上教程删除了Python2和yum。
1、删除现有Python
rpm -qa|grep python|xargs rpm -ev --allmatches --nodeps whereis python |xargs rm -frv whereis python
2、删除现有的yum
rpm -qa|grep yum|xargs rpm -ev --allmatches --nodeps whereis yum |xargs rm -frv
结果发现后面安装Python3需要yum，于是只能重装Python2和yum
1、查看本机CentOS版本
cat /etc/redhat-release
结果：CentOS Linux release 7.8.2003 (Core)
2、创建python和yum两个文件夹
mkdir /usr/local/src/python mkdir /usr/local/src/yum
3、根据上面版本7.8.2003
访问：https://vault.centos.org/7.8.2003/os/x86_64/Packages/
下载下面文件，放到/usr/local/src/python：
dbus-python-devel-1.1.1-9.el7.x86_64.rpm python-2.7.5-88.el7.x86_64.rpm python-iniparse-0.4-9.el7.noarch.rpm python-libs-2.7.5-88.el7.x86_64.rpm python-pycurl-7.19.0-19.el7.x86_64.rpm python-urlgrabber-3.10-10.el7.noarch.rpm rpm-python-4.11.3-43.el7.x86_64.rpm
下载下面文件，放到/usr/local/src/yum
yum-3.4.3-167.el7.centos.noarch.rpm yum-metadata-parser-1.1.4-10.el7.x86_64.rpm yum-plugin-fastestmirror-1.1.31-53.el7.noarch.rpm
4、安装python
cd /usr/local/src/python
rpm -ivh python-* rpm-python-*
如果出现安装包依赖问题，执行
rpm -ivh python-* rpm-python-* --nodeps --force
5、安装yum
cd /usr/local/src/yum rpm -ivh yum-*
安装Python3.7
1.安装编译工具和依赖环境等
yum -y groupinstall "Development tools" yum -y install zlib-devel bzip2-devel openssl-devel ncurses-devel sqlite-devel readline-devel tk-devel gdbm-devel db4-devel libpcap-devel xz-devel yum install libffi-devel -y
2.下载Python3安装包、解压
wget https://www.python.org/ftp/python/3.7.0/Python-3.7.0.tar.xz tar -zxvf Python-3.7.0.tar.xz
3.编译安装
mkdir /usr/local/python3 cd Python-3.7.0 ./configure --prefix=/usr/local/python3 make && make install
4.建立软连接
ln -s /usr/local/python3/bin/python3 /usr/local/bin/python3 ln -s /usr/local/python3/bin/pip3 /usr/local/bin/pip3
5.验证是否成功
python3 -V
pip3 -V