1.查看python版本
python --verstion，或python3 -V
2.查看python版本指向
ls -l /usr/bin | grep python
此命令信息较详细，也可使用简洁命令：ls /usr/bin/python*
3.直接升级
从版本2升级到3，可使用命令：apt-get install python3.7。若报错，只能从源码安装。
若报此错E: Couldn't find any package by regex 'python3.7-dev'则sudo add-apt-repository ppa:deadsnakes/ppa
sudo apt-get update
sudo apt-get install python3.7
或
sudo add-apt-repository ppa:jonathonf/python-3.7
sudo apt-get update
sudo apt-get install python3.7
若上述运行sudo add-apt-repository ppa:deadsnakes/ppa 出现 “bash: add-apt-repository: command not found” 则先运行：
sudo apt-get install -y software-properties-common
4.切换python版本
update-alternatives --list python#查看可替代python版本，如果报错没有可替代版本，则需要更新替代列表（操作如下）
update-alternatives --install /usr/bin/python python /usr/bin/python2.7 1
update-alternatives --install /usr/bin/python python /usr/bin/python3.5 2
若报错：update-alternatives: error: no alternatives for python，说明python 的替代版本尚未被 update-alternatives 命令识别，要更新一下替代列表，将 python2.7 和 python3.*放入其中。
# update-alternatives --install /usr/bin/python python /usr/bin/python2.7 1
update-alternatives: using /usr/bin/python2.7 to provide /usr/bin/python (python) in auto mode
# update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.4 2
update-alternatives: using /usr/bin/python3.4 to provide /usr/bin/python (python) in auto mode
加入新版python3.12的地址是，要使用真实地址，查找方法：which python3.12，即：/usr/local/bin/python3.12
也可移除代替版本：
# update-alternatives --remove python /usr/bin/python2.7
update-alternatives: removing manually selected alternative - switching python to auto mode
update-alternatives: using /usr/bin/python3.4 to provide /usr/bin/python (python) in auto mode
5.进行切换
update-alternatives --config python#选择标号
6.换链接指向
直接输入python3会链接指向默认python文件夹，可修改的。若之前python3指向python3.6.9，现修改成python3.7.1。
6.1查看python命令指向
ls -l /usr/bin | grep python3
6.2删除原有链接
rm /usr/bin/python3
6.3查找python3.7.1文件夹路径
不一定全在/usr/bin下，which python3
6.4建立新链接
ln -s /usr/bin/python3.7.1 /usr/bin/python3
6.5验证
python3
7.源码安装python3.12.0
1.更新源及依赖
sudo apt-get update
sudo apt-get install zlib1g-dev libbz2-dev libssl-dev libncurses5-dev libsqlite3-dev libreadline-dev tk-dev libgdbm-dev libdb-dev libpcap-dev xz-utils libexpat1-dev liblzma-dev libffi-dev libc6-dev
2.下载Python源代码
wget https://www.python.org/ftp/python/3.12.0/Python-3.12.0.tgz
3.解压并进入目录
解压tar -xzf Python-3.12.0.tgz，进入cd Python-3.12.0
4.配置安装位置
sudo ./configure --prefix=/usr/local/python3.12
若出现：If you want a release build with all stable optimizations active (PGO, etc), please run ./configure --enable-optimizations
则执行sudo ./configure --enable-optimizations
5.编译
sudo make
6.安装
sudo make install
7.验证
若最后出现：Successfully installed pip-23.2.1，即安装成功，此时可以输入python3 -V验证，一般不需要软连接，也就是说会自动更新pip3。
8.总结
为了减少安装量，最开始，也可以不执行步骤1，若在步骤6中报错ModuleNotFoundError: No module named _ctypes，执行如下：
sudo apt-get update
sudo apt-get upgrade
sudo apt-get dist-upgrade
sudo apt-get install build-essential python-dev python-setuptools python-pip python-smbus build-essential libncursesw5-dev libgdbm-dev libc6-dev zlib1g-dev libsqlite3-dev tk-dev libssl-dev openssl libffi-dev
再执行步骤6：sudo make install