ROS 1 and Python 3.10's deprecation of distutils.core

[sloretz]

@Mike_Purvis

which makes sense of course, since distutils is part of the stdlib and therefore should never fail to import.

@Arne

I did a quick & dirty grep over the repositories you get via “rosinstall_generator desktop_full --rosdistro noetic --deps --upstream” and found that it seems that a lot of core packages already changed their import in their setup.py files to solely use the “from setuptools import setup” statement.
But don’t use the try…except block. I would like to keep doing this as it should guarantee that nothing breaks on “really old” systems.

Before Noetic was released, many packages were switched to setuptools because distutils was split into a separate package in Debian Buster and Ubuntu Focal. If I recall correctly, the distutils import will only work on Focal if python3-distutils is installed. See this and linked PRs:
Prefer setuptools with Python 3 by sloretz · Pull Request #1048 · ros/catkin · GitHub.

I think it’s safer to assume setuptools is available rather than distutils because Catkin only exports a dependency on setuptools. Adding the buildtool_depend on python-setuptools was only required if one was trying to support Melodic and Noetic on the same branch.