我面临这个问题：
sudo apt-get install python3-pip
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
这是我面临的错误
我已经尝试过这些命令apt-get update&&apt-get upgrade
但是问题没有解决。