python-nbconvert fails to build with Python 3.9.0a5.

+ sphinx-build-3 docs/source html
Running Sphinx v2.2.2

Configuration error:
There is a programmable error in your configuration file:

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/nbconvert-5.6.0/docs/source/conf.py", line 25, in <module>
    exec(compile(f.read(), 'autogen_config.py', 'exec'), {})
  File "autogen_config.py", line 11, in <module>
  File "/builddir/build/BUILD/nbconvert-5.6.0/nbconvert/__init__.py", line 4, in <module>
    from .exporters import *
  File "/builddir/build/BUILD/nbconvert-5.6.0/nbconvert/exporters/__init__.py", line 3, in <module>
    from .html import HTMLExporter
  File "/builddir/build/BUILD/nbconvert-5.6.0/nbconvert/exporters/html.py", line 14, in <module>
    from nbconvert.filters.highlight import Highlight2HTML
  File "/builddir/build/BUILD/nbconvert-5.6.0/nbconvert/filters/__init__.py", line 7, in <module>
    from .strings import *
  File "/builddir/build/BUILD/nbconvert-5.6.0/nbconvert/filters/strings.py", line 22, in <module>
    from defusedxml import cElementTree as ElementTree
  File "/usr/lib/python3.9/site-packages/defusedxml/cElementTree.py", line 10, in <module>
    from xml.etree.cElementTree import TreeBuilder as _TreeBuilder
ModuleNotFoundError: No module named 'xml.etree.cElementTree'

Even thou the exception is from defusedxml (bz1817700), this import itself probably needs to be adapted:

   from defusedxml import cElementTree as ElementTree

See https://docs.python.org/3.9/whatsnew/3.9.html#removed

"The xml.etree.cElementTree module has been removed."



For the build logs, see:
https://copr-be.cloud.fedoraproject.org/results/@python/python3.9/fedora-rawhide-x86_64/01321094-python-nbconvert/

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

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.