我运行sudo apt-get install python3-venv然后得到。
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
python3-venv : Depends: python3.6-venv (>= 3.6.5-2~) but it is not going to be installed
Depends: python3 (= 3.6.5-3) but 3.6.7-1~18.04 is to be installed
E: Unable to correct problems, you have held broken packages.
我敢肯定，尝试重新安装Python是一件坏事，所以我无处可去。
python -V返回2.7.17，而python3 -V返回3.6.9。