为什么 libpython3.6 没有安装？

sudo apt-get install libpython3.6
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:
 libpython3.6 : Depends: libpython3.6-stdlib (= 3.6.6-1~18.04) but 3.6.6-1+xenial1 is to be installed
E: Unable to correct problems, you have held broken packages.

libpython3.6:
  Installed: (none)
  Candidate: 3.6.6-1~18.04
  Version table:
     3.6.6-1~18.04 500
        500 http://bd.archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages
     3.6.5-3 500
        500 http://bd.archive.ubuntu.com/ubuntu bionic/main amd64 Packages

libpython3.6-stdlib：已安装：3.6.6-1+xenial1 候选：3.6.6-1+xenial1 版本表：*** 3.6.6-1+xenial1 100 100 /var/lib/dpkg/status 3.6.6 -1~18.04 500 500 http://bd.archive.ubuntu.com/ubuntu bionic-updates/main amd64 包 3.6.5-3 500 500 http://bd.archive.ubuntu.com/ubuntu bionic/main amd64套餐