Python 2/3 version conflict

[jspricke]

Both provide the same files. This is needed to upgrade from Ubuntu 18 to
20.

[clalancette]

This seems reasonable to me, but I'm not that familiar with stdeb stuff. So I'll approve, but wait for someone else to also approve and merge.

[jspricke]

@clalancette me neither, but there is a similar construct here ;): https://github.com/ros-infrastructure/catkin_pkg/blob/master/stdeb.cfg#L12

[wjwwood]

lgtm, sorry for the delay

[wjwwood]

Actually wait, why do we need this? I thought that as long as it was just the python module, it would be separated by the different python site paths. @jspricke Are there particular files which are colliding?

[jspricke]

Both ship:

/usr/share/ament_index/resource_index/packages/osrf_pycommon
/usr/share/osrf_pycommon/package.xml

So if you want to upgrade from a bionic system with python-osrf-pycommon installed, you get:

Unpacking python3-osrf-pycommon (0.1.9-1) ...
dpkg: error processing archive /tmp/apt-dpkg-install-KldBzT/5-python3-osrf-pycommon_0.1.9-1_all.deb (--unpack):
 trying to overwrite '/usr/share/ament_index/resource_index/packages/osrf_pycommon', which is also in package python-osrf-pycommon 0.1.9-1
Errors were encountered while processing:
 /tmp/apt-dpkg-install-KldBzT/5-python3-osrf-pycommon_0.1.9-1_all.deb

With the conflict in place apt will remove python-osrf-pycommon before unpacking python3-osrf-pycommon and you can upgrade.