package python-psycopg2 2.6.1-1build2 failed to install/upgrade: sub-processo script pre-removal instalado retornou estado de saída de erro 1

[Claudia Enk de Aguiar]

Updated from python version 2.7 to 3.5 and removed the former from the alternatives list. It broke python-psycopg2 package so that I could not either finish installation or remove the package, and I got warnings every time I installed other packages through apt or updated apt sources, and various crashes reports on startup.

Adding python 2.7 to alternatives again, with priority set to 2 ($ sudo update-alternatives --install /usr/bin/python python /usr/bin/python2.7 2) restored normal behavior, but it took me a bit to understand what to do.

Maybe there could be a better warning or error message that pointed the user to the right direction.

ProblemType: Package
DistroRelease: Ubuntu 16.04
Package: python-psycopg2 2.6.1-1build2
ProcVersionSignature: Ubuntu 4.4.0-81.104-generic 4.4.67
Uname: Linux 4.4.0-81-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.6
Architecture: amd64
Date: Tue Jun 27 15:46:57 2017
ErrorMessage: sub-processo script pre-removal instalado retornou estado de saída de erro 1
InstallationDate: Installed on 2016-12-06 (203 days ago)
InstallationMedia: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
RelatedPackageVersions:
 dpkg 1.18.4ubuntu1.2
 apt 1.2.20
SourcePackage: psycopg2
Title: package python-psycopg2 2.6.1-1build2 failed to install/upgrade: sub-processo script pre-removal instalado retornou estado de saída de erro 1
UpgradeStatus: No upgrade log present (probably fresh install)