error:
Reading package lists… Done
Building dependency tree
Reading state information… Done
Package python3-pip is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package ‘python3-pip‘ has no installation candidate
解决方法：
添加 Universe 存储库：
sudo add-apt-repository universe更新apt:
sudo apt update
安装pip:
sudo apt install python3-pip
