upgrade to "20.04" crashes due to: "python-is-python2"

[PIPO]

  MarkInstall python-is-python2:amd64 < none -> 2.7.17-4 @un uN Ib > FU=1
  Installing python2 as Depende of python-is-python2
    MarkInstall python2:amd64 < none -> 2.7.17-2ubuntu4 @un uN Ib > FU=0
    Installing python2-minimal as PreDepende of python2
      MarkInstall python2-minimal:amd64 < none -> 2.7.17-2ubuntu4 @un uN Ib > FU=0
       Removing: python-minimal
        MarkDelete python-minimal:amd64 < 2.7.15~rc1-1 @ii mK > FU=0
    Installing libpython2-stdlib as Depende of python2
      MarkInstall libpython2-stdlib:amd64 < none -> 2.7.17-2ubuntu4 @un uN Ib > FU=0
       Removing: libpython-stdlib
        MarkDelete libpython-stdlib:amd64 < 2.7.15~rc1-1 @ii mK > FU=0
     Removing: python
      MarkDelete python:amd64 < 2.7.15~rc1-1 @ii mK Ib > FU=0
Starting pkgProblemResolver with broken count: 1
Starting 2 pkgProblemResolver with broken count: 1
Investigating (0) nodejs:amd64 < 12.18.4-1nodesource1 @ii mK Ib >
Broken nodejs:amd64 Depende on python-minimal:amd64 < 2.7.15~rc1-1 @ii gR >
  Considering python-minimal:amd64 1 as a solution to nodejs:amd64 92
  Added python-minimal:amd64 to the remove list
  Fixing nodejs:amd64 via keep of python-minimal:amd64
  MarkKeep python-minimal:amd64 < 2.7.15~rc1-1 @ii gR > FU=0
Investigating (0) python2-minimal:amd64 < none -> 2.7.17-2ubuntu4 @un umN Ib >
Broken python2-minimal:amd64 Rompe on python-minimal:amd64 < 2.7.15~rc1-1 @ii gK > (< 2.7.15-2)
  Considering python-minimal:amd64 1 as a solution to python2-minimal:amd64 1
  MarkKeep python2-minimal:amd64 < none -> 2.7.17-2ubuntu4 @un umN Ib > FU=0
  Holding Back python2-minimal:amd64 rather than change python-minimal:amd64
Investigating (0) python2:amd64 < none -> 2.7.17-2ubuntu4 @un umN Ib >
Broken python2:amd64 PreDepende on python2-minimal:amd64 < none | 2.7.17-2ubuntu4 @un umH > (= 2.7.17-2ubuntu4)
  Considering python2-minimal:amd64 1 as a solution to python2:amd64 1
  MarkKeep python2:amd64 < none -> 2.7.17-2ubuntu4 @un umN Ib > FU=0
  Holding Back python2:amd64 rather than change python2-minimal:amd64
Investigating (1) python-is-python2:amd64 < none -> 2.7.17-4 @un pumN Ib >
Broken python-is-python2:amd64 Depende on python2:amd64 < none | 2.7.17-2ubuntu4 @un umH >
  Considering python2:amd64 1 as a solution to python-is-python2:amd64 9999
  Re-Instated python2-minimal:amd64
  Re-Instated python2:amd64
Investigating (1) python2-minimal:amd64 < none -> 2.7.17-2ubuntu4 @un umN Ib >
Broken python2-minimal:amd64 Rompe on python-minimal:amd64 < 2.7.15~rc1-1 @ii gK > (< 2.7.15-2)
  Considering python-minimal:amd64 1 as a solution to python2-minimal:amd64 1
  MarkKeep python2-minimal:amd64 < none -> 2.7.17-2ubuntu4 @un umN Ib > FU=0
  Holding Back python2-minimal:amd64 rather than change python-minimal:amd64
Investigating (1) python2:amd64 < none -> 2.7.17-2ubuntu4 @un umN Ib >
Broken python2:amd64 PreDepende on python2-minimal:amd64 < none | 2.7.17-2ubuntu4 @un umH > (= 2.7.17-2ubuntu4)
  Considering python2-minimal:amd64 1 as a solution to python2:amd64 1
  MarkKeep python2:amd64 < none -> 2.7.17-2ubuntu4 @un umN Ib > FU=0
  Holding Back python2:amd64 rather than change python2-minimal:amd64
Investigating (2) python-is-python2:amd64 < none -> 2.7.17-4 @un pumN Ib >
Broken python-is-python2:amd64 Depende on python2:amd64 < none | 2.7.17-2ubuntu4 @un umH >
  Considering python2:amd64 1 as a solution to python-is-python2:amd64 9999
Done
Log time: 2020-10-05 03:55:54.164121

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.38 [origin: unknown]
ProcVersionSignature: Ubuntu 5.4.0-48.52~18.04.1-lowlatency 5.4.60
Uname: Linux 5.4.0-48-lowlatency x86_64
ApportVersion: 2.20.9-0ubuntu7.17
Architecture: amd64
CrashDB: ubuntu
Date: Mon Oct 5 03:52:26 2020
InstallationDate: Installed on 2018-09-21 (744 days ago)
InstallationMedia: Ubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
PackageArchitecture: all
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 LANG=es_ES.UTF-8
 SHELL=/bin/bash
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2020-10-05 (0 days ago)
VarLogDistupgradeAptlog:
 Log time: 2020-10-05 03:51:15.481933
 Log time: 2020-10-05 03:52:02.935666
VarLogDistupgradeTermlog:

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Daniel Feliciano Branco (danielblues)]

I had the same problem, but my log started like this:

Log time: 2020-10-21 09:38:03.264979
  MarkInstall python-is-python2:amd64 < none -> 2.7.17-4 @un uN Ib > FU=1
  Installing python2 as Depends of python-is-python2
    MarkInstall python2:amd64 < none -> 2.7.17-2ubuntu4 @un uN Ib > FU=0
    Installing python2-minimal as PreDepends of python2
      MarkInstall python2-minimal:amd64 < none -> 2.7.17-2ubuntu4 @un uN Ib > FU=0
       Removing: python-minimal
        MarkDelete python-minimal:amd64 < 2.7.15~rc1-1 @ii mK > FU=0
    Installing libpython2-stdlib as Depends of python2
      MarkInstall libpython2-stdlib:amd64 < none -> 2.7.17-2ubuntu4 @un uN Ib > FU=0
       Removing: libpython-stdlib
        MarkDelete libpython-stdlib:amd64 < 2.7.15~rc1-1 @ii mK > FU=0
     Removing: python
      MarkDelete python:amd64 < 2.7.15~rc1-1 @ii mK Ib > FU=0
Starting pkgProblemResolver with broken count: 1
Starting 2 pkgProblemResolver with broken count: 1
Investigating (0) python-support:amd64 < 1.0.15 @ii mK Ib >
>>> Broken python-support <<<:amd64 Depends on python-minimal:amd64 < 2.7.15~rc1-1 @ii gR >

I've purged python-support, and solved the problem (i.e. it's installing now). It had only 6 packages depending on it.
From your log "nodejs" might be the problem, maybe a leftover from some ppa. Proceed with caution when removing python packages.
Best,
Daniel

[Paul L Miller (paul+1945)]

I have the same problem but "Starting pkgProblemResolver with broken count: 1" has a count of 2.

[Paul L Miller (paul+1945)]

Here is the text that goes with #4:
 MarkDelete python-minimal:amd64 < 2.7.15~rc1-1 @ii mK > FU=1
  MarkDelete libpython-dev:amd64 < 2.7.15~rc1-1 @ii gK > FU=1
  MarkDelete libpython-stdlib:amd64 < 2.7.15~rc1-1 @ii mK > FU=1
  MarkInstall python-is-python2:amd64 < none -> 2.7.17-4 @un umN Ib > FU=1
  Installing python2 as Depends of python-is-python2
    MarkInstall python2:amd64 < none -> 2.7.17-2ubuntu4 @un uN Ib > FU=0
    Installing python2-minimal as PreDepends of python2
      MarkInstall python2-minimal:amd64 < none -> 2.7.17-2ubuntu4 @un uN > FU=0
    Installing libpython2-stdlib as Depends of python2
      MarkInstall libpython2-stdlib:amd64 < none -> 2.7.17-2ubuntu4 @un uN > FU=0
     Removing: python
      MarkDelete python:amd64 < 2.7.15~rc1-1 @ii mK Ib > FU=0
Starting pkgProblemResolver with broken count: 2
Starting 2 pkgProblemResolver with broken count: 2

This is at the head of apt.log just after the first three lines which are timestamps.