python-rosdep fails to build with Python 3.9.0a5.

Traceback (most recent call last):
  File "/usr/lib/python3.9/site-packages/sphinx/config.py", line 361, in eval_config_file
    execfile_(filename, namespace)
  File "/usr/lib/python3.9/site-packages/sphinx/util/pycompat.py", line 81, in execfile_
    exec(code, _globals)
  File "/builddir/build/BUILD/rosdep-0.17.1/doc/conf.py", line 21, in <module>
    from rosdep2 import __version__  # noqa
  File "../src/rosdep2/__init__.py", line 40, in <module>
    from .installers import InstallerContext, Installer, \
  File "../src/rosdep2/installers.py", line 36, in <module>
    from rospkg.os_detect import OsDetect
  File "/usr/lib/python3.9/site-packages/rospkg/__init__.py", line 42, in <module>
    from .rospack import expand_to_packages, get_package_name, \
  File "/usr/lib/python3.9/site-packages/rospkg/rospack.py", line 35, in <module>
    from xml.etree.cElementTree import ElementTree
ModuleNotFoundError: No module named 'xml.etree.cElementTree'

This is caused by bz1817942.

For the build logs, see:
https://copr-be.cloud.fedoraproject.org/results/@python/python3.9/fedora-rawhide-x86_64/01321107-python-rosdep/

For all our attempts to build python-rosdep with Python 3.9, see:
https://copr.fedorainfracloud.org/coprs/g/python/python3.9/package/python-rosdep/

Testing and mass rebuild of packages is happening in copr. You can follow these instructions to test locally in mock if your package builds with Python 3.9:
https://copr.fedorainfracloud.org/coprs/g/python/python3.9/

Let us know here if you have any questions.

Python 3.9 will be included in Fedora 33. To make that update smoother, we're building Fedora packages with early pre-releases of Python 3.9.
A build failure prevents us from testing all dependent packages (transitive [Build]Requires), so if this package is required a lot, it's important for us to get it fixed soon.
We'd appreciate help from the people who know this package best, but if you don't want to work on this now, let us know so we can try to work around it on our side.