ubuntu 18.04，20.04 都能用，安装python3.9.4 + pip21.1.1（亲测新版python3.9.7+pip21.2.3也可以用）

安装python3.9.4

sudo apt-get update
sudo apt-get install build-essential zlib1g-dev libncurses5-dev libgdbm-dev libnss3-dev libssl-dev libreadline-dev libffi-dev libsqlite3-dev
sudo wget https://www.python.org/ftp/python/3.9.4/Python-3.9.4.tgz

root@062e241f5835:/# wget https://www.python.org/ftp/python/3.9.4/Python-3.9.4.tgz
–2021-05-02 08:49:19-- https://www.python.org/ftp/python/3.9.4/Python-3.9.4.tgz
Resolving www.python.org (www.python.org)… 151.101.108.223, 2a04:4e42:1a::223
Connecting to www.python.org (www.python.org)|151.101.108.223|:443… connected.
HTTP request sent, awaiting response… 200 OK
Length: 25411523 (24M) [application/octet-stream]
Saving to: ‘Python-3.9.4.tgz’

Python-3.9.4.tgz 100%[===================>] 24.23M 720KB/s in 39s

2021-05-02 08:49:59 (631 KB/s) - ‘Python-3.9.4.tgz’ saved [25411523/25411523]

解压源码包：

tar -zxvf Python-3.9.4.tgz

进入解压后的目录：

cd Python-3.9.4

./configure  --prefix=/usr/local
./configure --enable-optimizations

这里的–prefix=/usr/local用于指定安装目录（建议指定）。如果不指定，就会使用默认的安装目录。
–enable-optimizations选项通过运行多个测试来优化Python二进制文件。这会使构建过程变慢。

启动Python 3.9.4构建过程：

sudo make -j 8

构建过程完成后，输入以下命令安装Python二进制文件：

sudo make install

删除原先的命令，并建立新的软连接

rm -rf /usr/bin/python3
ln -s /usr/local/bin/python3 /usr/bin/python3

查看安装完成版本：

python3.9 --version

安装pip3

sudo apt-get install python3-pip

升级pip3 （目前最新pip21.1.1）

sudo pip3 install --upgrade pip

root@062e241f5835:/Python-3.9.4# pip3 install --upgrade pip
Collecting pip
Downloading https://files.pythonhosted.org/packages/cd/6f/43037c7bcc8bd8ba7c9074256b1a11596daa15555808ec748048c1507f08/pip-21.1.1-py3-none-any.whl (1.5MB)
100% |################################| 1.6MB 489kB/s
Installing collected packages: pip
Found existing installation: pip 9.0.1
Not uninstalling pip at /usr/lib/python3/dist-packages, outside environment /usr
Successfully installed pip-21.1.1
root@062e241f5835:/Python-3.9.4#

 pip3 -V