1. 安装依赖关系

yum install -y libffi-devel 

2. 下载和安装python包

cd /usr/local/src
wget https://www.python.org/ftp/python/3.9.5/Python-3.9.5.tgz
tar zxvf Python-3.9.5.tgz
cd Python-3.9.5/
./configure --prefix=/usr/local/python3.9 --with-ssl
make && make install

3. 修改软连接

1. ln -fs /usr/local/python3.9/bin/python3.9 /usr/bin/python
   ln -fs /usr/local/python3.9/bin/python3.9 /usr/bin/python3
   ln -fs /usr/local/python3.9/bin/pip3.9 /usr/bin/pip
   ln -fs /usr/local/python3.9/bin/pip3.9 /usr/bin/pip3
   
   

2. 5.修改yum文件

3. vi /usr/bin/yum
   vi /usr/libexec/urlgrabber-ext-down 第一行改都修改为: (原因是安装了python3.8,CentOS 7.X 自带的yum采用的是python2.X，当系统将python升级到2.7 或3.X后，出现语法解释错误)

4. #!/usr/bin/python2.7

5. 6.升级pip

6. python -m pip install --upgrade pip

出现错误必须：

ln -fs /usr/local/python3.9/bin/python3.9 /usr/bin/python
ln -fs /usr/local/python3.9/bin/python3.9 /usr/bin/python3
ln -fs /usr/local/python3.9/bin/pip3.9 /usr/bin/pip
ln -fs /usr/local/python3.9/bin/pip3.9 /usr/bin/pip3

必须

# 顺手解决 Can't locate Tcl/Tk libs and/or headers
sudo yum install tcl-devel tk-devel
# 解决_ssl问题
sudo yum install openssl-devel

网上的加什么网关方法都是不行的记住了，忙了半个小时