package python3.6 3.6.8-1~18.10 failed to install/upgrade: installed python3.6 package post-installation script subprocess returned error exit status 127

[Harel Malka]

This is after a reinstall of python 3.6.
The reason this was reinstalled is trying to fix an upgrade error with do-release-upgrade (or with the gui) resulting in a python3 symlink corrupted error. This is with default python 3.6 of ubuntu 18.10.

$ lsb_release -rd
Description: Ubuntu 18.10
Release: 18.10

$ apt-cache policy python3.6
python3.6:
  Installed: 3.6.8-1~18.10
  Candidate: 3.6.8-1~18.10
  Version table:
 *** 3.6.8-1~18.10 500
        500 http://gb.archive.ubuntu.com/ubuntu cosmic-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     3.6.7~rc1-1 500
        500 http://gb.archive.ubuntu.com/ubuntu cosmic/main amd64 Packages

This happened without any intervention from me - just a random error and report request.
However, this is the result of what is described above and in more details:

1. Attempted to upgrade to 19.04 via software centre and cmd line, always with this error:

Reading cache

Checking package manager

Cannot upgrade

Your python3 install is corrupted. Please fix the '/usr/bin/python3'
symlink.

Note that python3 is the default 3.6, it was never changed. Symlink was fine.

Followed good and bad advice. Last one was the first comment here; https://dev1galaxy.org/viewtopic.php?id=649

The result was a messed up python symlink, which overwrote the binary.

Removed, reinstalled and this error just popped up. Technically so far things work though but i still cannot upgrade.

ProblemType: Package
DistroRelease: Ubuntu 18.10
Package: python3.6 3.6.8-1~18.10
ProcVersionSignature: Ubuntu 4.18.0-18.19-generic 4.18.20
Uname: Linux 4.18.0-18-generic x86_64
ApportVersion: 2.20.10-0ubuntu13.3
AptOrdering:
 python3.6:amd64: Install
 NULL: ConfigurePending
Architecture: amd64
Date: Fri May 24 17:24:14 2019
DuplicateSignature:
 package:python3.6:3.6.8-1~18.10
 Setting up python3.6 (3.6.8-1~18.10) ...
 /var/lib/dpkg/info/python3.6.postinst: 9: /var/lib/dpkg/info/python3.6.postinst: /usr/bin/python3.6: not found
 dpkg: error processing package python3.6 (--configure):
  installed python3.6 package post-installation script subprocess returned error exit status 127
ErrorMessage: installed python3.6 package post-installation script subprocess returned error exit status 127
InstallationDate: Installed on 2018-12-15 (160 days ago)
InstallationMedia: Ubuntu 18.10 "Cosmic Cuttlefish" - Release amd64 (20181017.3)
Python3Details: /usr/bin/python3, Python 3.6.7, python3-minimal, 3.6.7-1~18.10
PythonDetails: /usr/bin/python3, Python 3.6.7, python-minimal, 2.7.15-3
RelatedPackageVersions:
 dpkg 1.19.0.5ubuntu5
 apt 1.7.4
SourcePackage: python3.6
Title: package python3.6 3.6.8-1~18.10 failed to install/upgrade: installed python3.6 package post-installation script subprocess returned error exit status 127
UpgradeStatus: Upgraded to cosmic on 2019-05-24 (0 days ago)