roslaunch reinstallation

edit

Hey there,

While I was trying to fix my rqt problem (but that's another post) I sudo apt purge rqt and then sudo apt autoremove and update. Now I have broken apparently roslaunch :/

Here are the subsequent commands and their outputs:

roscore

The program 'roscore' is currently not installed. You can install it by typing:
sudo apt install python-roslaunch

then:

sudo apt install python-roslaunch

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:
 python-roslaunch : Depends: python-roslib but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

then:

sudo apt install python-roslib

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:
 python-roslib : Depends: catkin but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

And it goes on like this for

sudo apt install catkin --> Depends: python-catkin-pkg but it is not going to be installed

sudo apt install python-catkin-pkg

where it says its already there:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
python-catkin-pkg is already the newest version (0.3.1-1).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

What is wrong with that? Can anybody help me with this?

Thanks in advance!