Purpose, documentation of python-ros* packages

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Can't find purpose and documentation of these packages if anything.

I noticed (awhile ago honestly though) there are many python-ros* packages available from apt repo, much more than a few of them that are known from some common usecases (rosdistro, rospkg, rosinstall*). On my Ubuntu 18.04 I see:

$ cat /etc/apt/sources.list.d/ros-latest.list
deb http://packages.ros.org/ros/ubuntu bionic main

$ sudo apt-get install python-ros[TAB]
python-rosbag                 python-roscreate              python-rosgraph-msgs          python-rosmake                python-rospkg-modules         python-roswtf
python-rosboost-cfg           python-rosdep                 python-rosinstall             python-rosmaster              python-rospy                  
python-ros-buildfarm          python-rosdep2                python-rosinstall-generator   python-rosmsg                 python-rosservice             
python-ros-buildfarm-modules  python-rosdistro              python-roslaunch              python-rosnode                python-rostest                
python-rosclean               python-rosdistro-modules      python-roslib                 python-rosparam               python-rostopic               
python-roscpp-msgs            python-rosgraph               python-roslz4                 python-rospkg                 python-rosunit

Looking at some of them, the version of these python-ros* might look older than the latest available from each ROS distro. E.g. for rospy (ATM the latest release seems to be 1.14.3),

$ apt-cache policy ros-melodic-rospy
ros-melodic-rospy:
  Installed: (none)
  Candidate: 1.14.3-0bionic.20190601.011442
  Version table:
     1.14.3-0bionic.20190601.011442 500
        500 http://packages.ros.org/ros/ubuntu bionic/main amd64 Packages

$ apt-cache policy python-rospy
python-rospy:
  Installed: (none)
  Candidate: 1.13.5+ds1-3
  Version table:
     1.13.5+ds1-3 500
        500 http://us.archive.ubuntu.com/ubuntu bionic/universe amd64 Packages
        500 http://us.archive.ubuntu.com/ubuntu bionic/universe i386 Packages

My guess is as follows:

• Each package in ros_comm are packaged as installable from standard debian/Ubuntu repository.
• Released only once per Linux distro?