python dependencies cannot be installed before installing qgis

[jean marius]

marius@marius-ThinkPad-T440s:~$ sudo apt-get install qgis python-qgis qgis-plugin-grass libgdal-dev
Reading package lists... Done
Building dependency tree
Reading state information... Done
libgdal-dev is already the newest version.
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:
 python-qgis : Depends: python-qt4-sql but it is not installable
               Depends: python-qgis-common (= 1:2.18.1+20trusty-ubuntugis) but it is not going to be installed
               Depends: python-psycopg2 but it is not installable
               Depends: python-jinja2 but it is not installable
               Depends: python-markupsafe but it is not installable
               Depends: python-dateutil but it is not installable
               Depends: libqgispython2.18.1 but it is not going to be installed
               Depends: libqgis-analysis2.18.1 but it is not going to be installed
               Depends: libqgis-core2.18.1 but it is not going to be installed
               Depends: libqgis-gui2.18.1 but it is not going to be installed
               Depends: libqgis-networkanalysis2.18.1 but it is not going to be installed
               Depends: libqgis-server2.18.1 but it is not going to be installed
               Recommends: liblwgeom-dev but it is not going to be installed
 qgis : Depends: libqgis-analysis2.18.1 but it is not going to be installed
        Depends: libqgis-app2.18.1 but it is not going to be installed
        Depends: libqgis-core2.18.1 but it is not going to be installed
        Depends: libqgis-gui2.18.1 but it is not going to be installed
        Depends: libqgis-networkanalysis2.18.1 but it is not going to be installed
        Depends: qgis-providers (= 1:2.18.1+20trusty-ubuntugis) but it is not going to be installed
        Recommends: qgis-provider-grass but it is not going to be installed
 qgis-plugin-grass : Depends: qgis-provider-grass (= 1:2.18.1+20trusty-ubuntugis) but it is not going to be installed
                     Depends: libqgis-app2.18.1 but it is not going to be installed
                     Depends: libqgis-core2.18.1 but it is not going to be installed
                     Depends: libqgis-gui2.18.1 but it is not going to be installed
                     Depends: libqgisgrass7-2.18.1 but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: linux-image-4.4.0-53-generic 4.4.0-53.74~14.04.1
ProcVersionSignature: Ubuntu 4.4.0-53.74~14.04.1-generic 4.4.30
Uname: Linux 4.4.0-53-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.21
Architecture: amd64
CurrentDesktop: Unity
Date: Tue Dec 6 17:53:43 2016
InstallationDate: Installed on 2016-11-24 (12 days ago)
InstallationMedia: Ubuntu 14.04.3 LTS "Trusty Tahr" - Beta amd64 (20150805)
SourcePackage: linux-lts-xenial
UpgradeStatus: No upgrade log present (probably fresh install)

[Eric Desrochers (slashd)]

Jean-Marius,

Did you try to run :
$ sudo apt-get install -f

This will attempt to correct a system with broken dependencies in place. This option, when used with install/remove, can omit any packages to permit APT to deduce a likely solution.