所以我的 ubuntu 安装（16.04.6 LTS）在配置更新通知程序时遇到问题：
~$ sudo dpkg --configure -a
Setting up update-notifier-common (3.168.10) ...
Traceback (most recent call last):
File "/usr/lib/update-notifier/package-data-downloader", line 24, in <module>
import debian.deb822
File "/usr/lib/python3/dist-packages/debian/deb822.py", line 38, in <module>
import chardet
ImportError: No module named 'chardet'
dpkg: error processing package update-notifier-common (--configure):
subprocess installed post-installation script returned error exit status 1
dpkg: dependency problems prevent configuration of update-notifier:
update-notifier depends on update-notifier-common (= 3.168.10); however:
Package update-notifier-common is not configured yet.
dpkg: error processing package update-notifier (--configure):
dependency problems - leaving unconfigured
dpkg: dependency problems prevent configuration of ubuntu-desktop:
ubuntu-desktop depends on update-notifier; however:
Package update-notifier is not configured yet.
dpkg: error processing package ubuntu-desktop (--configure):
dependency problems - leaving unconfigured
Errors were encountered while processing:
update-notifier-common
update-notifier
ubuntu-desktop
因此，看来我需要 chadet 才能使此配置正常工作。尝试安装它时，告诉我它已安装：
$ sudo apt-get install python-chardet
Reading package lists... Done
Building dependency tree
Reading state information... Done
python-chardet is already the newest version (2.3.0-2).
0 upgraded, 0 newly installed, 0 to remove and 82 not upgraded.
3 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n] n
Abort.
不确定为什么 python (v.2.7.12) 找不到 chardet，有什么想法吗？
表示它也已为 Python 3 安装：
$ sudo apt install python3-chardet
Reading package lists... Done
Building dependency tree
Reading state information... Done
python3-chardet is already the newest version (2.3.0-2).
0 upgraded, 0 newly installed, 0 to remove and 82 not upgraded.
3 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n] n
Abort.
答案1
好的，找到问题了。经过一番折腾，我发现我有两个不同版本的 python3（3.5 和 3.6），而 /usr/bin 中的 python3 符号链接指向了错误的版本（3.5）。删除链接，重新生成指向 3.6 - 现在一切正常：
$ sudo dpkg --configure -a
Setting up update-notifier-common (3.168.10) ...
Setting up update-notifier (3.168.10) ...
Setting up ubuntu-desktop (1.361.3) ...
所以，从本质上讲，这是我之前对我的系统造成的错误。