update-alternatives --list python 查看当前可用python版本
log： update-alternatives: error: no alternatives for python
update-alternatives --install /usr/bin/python python /usr/bin/python2.7 2 添加python版本到list
log:
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 2 添加python3版本到list
update-alternatives --config python 选择python版本
update-alternatives --remove python /usr/bin/python2.7 移除list的python版本
