Ubuntu – Issue with python2 package not installable on Ubuntu 18.04

18.04aptdependenciespackage-management

Final update

Similar issue has been reported here.

Discourse announcement: Build/CI failures with ros-testing repository enabled?

Update2

Actually, installation of ROS Melodic failed at the end in my case:

Errors were encountered while processing:
 /tmp/apt-dpkg-install-lRVV2P/0767-python-catkin-pkg-modules_0.4.22-1_all.deb
 /tmp/apt-dpkg-install-lRVV2P/0794-python-rospkg-modules_1.2.8-1_all.deb
 /tmp/apt-dpkg-install-lRVV2P/0796-python-rosdistro-modules_0.8.2-1_all.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

More logs:

Selecting previously unselected package python-catkin-pkg-modules.
Preparing to unpack .../0767-python-catkin-pkg-modules_0.4.22-1_all.deb ...
Unpacking python-catkin-pkg-modules (0.4.22-1) ...
dpkg: error processing archive /tmp/apt-dpkg-install-lRVV2P/0767-python-catkin-pkg-modules_0.4.22-1_all.deb (--unpack):
 trying to overwrite '/usr/lib/python2.7/dist-packages/catkin_pkg/__init__.py', which is also in package python-catkin-pkg 0.3.9-1

Selecting previously unselected package python-rospkg-modules.
Preparing to unpack .../0794-python-rospkg-modules_1.2.8-1_all.deb ...
Unpacking python-rospkg-modules (1.2.8-1) ...
dpkg: error processing archive /tmp/apt-dpkg-install-lRVV2P/0794-python-rospkg-modules_1.2.8-1_all.deb (--unpack):
 trying to overwrite '/usr/lib/python2.7/dist-packages/rospkg/__init__.py', which is also in package python-rospkg 1.1.4-1

Selecting previously unselected package python-rosdistro-modules.
Preparing to unpack .../0796-python-rosdistro-modules_0.8.2-1_all.deb ...
Unpacking python-rosdistro-modules (0.8.2-1) ...
dpkg: error processing archive /tmp/apt-dpkg-install-lRVV2P/0796-python-rosdistro-modules_0.8.2-1_all.deb (--unpack):
 trying to overwrite '/usr/lib/python2.7/dist-packages/rosdistro/__init__.py', which is also in package python-rosdistro 0.6.6-1

Update

When faulty:

The following packages have unmet dependencies:
 python-rosinstall-generator : Depends: python-catkin-pkg (>= 0.1.28) but it is not going to be installed
                               Depends: python-pkg-resources but it is not going to be installed
                               Depends: python-rosdistro (>= 0.7.3) but it is not going to be installed
                               Depends: python-rospkg but it is not going to be installed
                               Depends: python-yaml but it is not going to be installed
                               Depends: python2 (< 2.8) but it is not installable
                               Depends: python2 (>= 2.7) but it is not installable
                               Depends: python2:any (>= 2.6.6-7~) but it is not installable
E: Unable to correct problems, you have held broken packages.

apt-cache policy python-rosinstall-generator
python-rosinstall-generator:
  Installed: (none)
  Candidate: 0.1.20-1
  Version table:
     0.1.20-1 500
        500 http://packages.ros.org/ros/ubuntu bionic/main amd64 Packages
        500 http://packages.ros.org/ros/ubuntu bionic/main i386 Packages
     0.1.13-3 500
        500 http://archive.ubuntu.com/ubuntu bionic/universe amd64 Packages
        500 http://archive.ubuntu.com/ubuntu bionic/universe i386 Packages

apt-cache policy python3-rosinstall-generator
python3-rosinstall-generator:
  Installed: (none)
  Candidate: 0.1.20-1
  Version table:
     0.1.20-1 500
        500 http://packages.ros.org/ros/ubuntu bionic/main amd64 Packages
        500 http://packages.ros.org/ros/ubuntu bionic/main i386 Packages
     0.1.13-3 500
        500 http://archive.ubuntu.com/ubuntu bionic/universe amd64 Packages
        500 http://archive.ubuntu.com/ubuntu bionic/universe i386 Packages

I have some issue to install the following package python-rosinstall-generator on Ubuntu 18.04 with apt:

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-rosinstall-generator : Depends: python2 (< 2.8) but it is not installable
                               Depends: python2 (>= 2.7) but it is not installable
                               Depends: python2:any (>= 2.6.6-7~) but it is not installable
E: Unable to correct problems, you have held broken packages.

Since I am using Docker, I have an old image where python-rosinstall-generator has been successfully installed with apt install python-rosinstall-generator:

apt-cache depends python-rosinstall-generator
python-rosinstall-generator
  Depends: python
  Depends: python
  Depends: python-catkin-pkg
  Depends: python-pkg-resources
  Depends: python-rosdistro
  Depends: python-rospkg
  Depends: python-yaml
  Depends: <python:any>
    python:i386
    python
  Depends: <python-argparse>
    libpython2.7-stdlib
  Conflicts: python3-rosinstall-generator

After doing apt update in the Docker, it gives now:

apt-cache depends python-rosinstall-generator
python-rosinstall-generator
  Depends: python-catkin-pkg
  Depends: python-pkg-resources
  Depends: python-rosdistro
  Depends: python-rospkg
  Depends: python-yaml
  Depends: <python2>
  Depends: <python2>
  Depends: <python2:any>
  Depends: <python-argparse>
    libpython2.7-stdlib
  Conflicts: python3-rosinstall-generator

And python2 package cannot be installed:

apt install python2
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package python2 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'python2' has no installation candidate

It looks like a recent update has broken something, and has introduced a python2 package dependency.

dockerfile

FROM ubuntu:18.04

ENV DEBIAN_FRONTEND=noninteractive
RUN apt-get update && apt-get install --yes \
    build-essential \
    software-properties-common \
    pkg-config \
    cmake \
    g++

RUN add-apt-repository "deb http://archive.ubuntu.com/ubuntu $(lsb_release -sc) main universe restricted multiverse"

RUN echo "deb http://packages.ros.org/ros/ubuntu $(lsb_release -sc) main" > /etc/apt/sources.list.d/ros-latest.list
RUN apt-key adv --keyserver 'hkp://keyserver.ubuntu.com:80' --recv-key C1CF6E31E6BADE8868B172B4F42ED6FBAB17C654
RUN apt-get update && apt-get install --yes python-rosinstall-generator

Best Answer

It looks like that packages.ros.org repository provides python3-rosinstall-generator package which is not compatible with Ubuntu 18.04 LTS.

The container creation using Dockerfile without such repository is successful:

FROM ubuntu:18.04

ENV DEBIAN_FRONTEND=noninteractive
RUN apt-get update && apt-get install --yes \
    build-essential \
    software-properties-common \
    pkg-config \
    cmake \
    g++

RUN apt-get update && apt-get install --yes python-rosinstall-generator

But installation of ros-melodic-desktop-full ends successfully using your original Dockerfile.

Related Question