已解决 - 无法在 (X)Ubuntu 18.10 中安装 python3.7-venv

Question

我刚刚将我的 XUbuntu 18.04 安装更新到 18.10（注意：由于某种原因，我do-release-upgrade在软件包仍在下载时停止了，然后我继续apt upgrade并重新启动，一切似乎都很好）。我通过包管理器安装了 python3.7 并尝试将其设为默认：

sudo update-alternatives --install /usr/bin/python python /usr/bin/python3.7 1
# This may not be needed for only 1 alternative, but does not hurt to run it:
sudo update-alternatives --config python

这就是问题：

$ sudo apt install python3.7-venv 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
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:
 python3.7-venv : Depends: python3.7 (= 3.7.1-1~18.10) but 3.7.1-1+bionic1 is to be installed
E: Unable to correct problems, you have held broken packages.

为什么它尝试使用仿生以及如何修复它？

我的系统已完全更新，刚刚运行apt update，并apt upgrade显示：0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

我的 /etc/apt/source.list （注意我手动删除了注释掉的 bionic 行来清理它）：

# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://hu.archive.ubuntu.com/ubuntu/ cosmic main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://hu.archive.ubuntu.com/ubuntu/ cosmic-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://hu.archive.ubuntu.com/ubuntu/ cosmic universe
deb http://hu.archive.ubuntu.com/ubuntu/ cosmic-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu 
## team, and may not be under a free licence. Please satisfy yourself as to 
## your rights to use the software. Also, please note that software in 
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://hu.archive.ubuntu.com/ubuntu/ cosmic multiverse
deb http://hu.archive.ubuntu.com/ubuntu/ cosmic-updates multiverse

## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://hu.archive.ubuntu.com/ubuntu/ cosmic-backports main restricted universe multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
deb http://archive.canonical.com/ubuntu cosmic partner

deb http://security.ubuntu.com/ubuntu cosmic-security main restricted
deb http://security.ubuntu.com/ubuntu cosmic-security universe
deb http://security.ubuntu.com/ubuntu cosmic-security multiverse
# deb [arch=amd64] https://download.docker.com/linux/ubuntu cosmic stable # disabled on upgrade to cosmic
# deb-src [arch=amd64] https://download.docker.com/linux/ubuntu bionic stable

注意：我也尝试过使用另一个镜像，sudo apt update但错误仍然一样。