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: Installed: 3.6.6-1+xenial1 Candidate: 3.6.6-1+xenial1 Version table: *** 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 Packages 3.6.5-3 500 500 http://bd.archive.ubuntu.com/ubuntu bionic/main amd64 Packages
apt-cache policy libpython3.6
output as an edit to your quesiton.apt-cache policy libpython3.6-stdlib
as well, but this time don't erase the other content in your question and just add it as an additional bit of information at the bottom?