python-mutagen fails to build with Python 3.9.0a2.

+ /usr/bin/python3 setup.py test
running test
Traceback (most recent call last):
  File "/builddir/build/BUILD/mutagen-1.42.0/setup.py", line 254, in <module>
    setup(cmdclass=cmd_classes,
  File "/usr/lib64/python3.9/distutils/core.py", line 148, in setup
    dist.run_commands()
  File "/usr/lib64/python3.9/distutils/dist.py", line 966, in run_commands
    self.run_command(cmd)
  File "/usr/lib64/python3.9/distutils/dist.py", line 985, in run_command
    cmd_obj.run()
  File "/builddir/build/BUILD/mutagen-1.42.0/setup.py", line 161, in run
    import tests
  File "/builddir/build/BUILD/mutagen-1.42.0/tests/__init__.py", line 16, in <module>
    from mutagen._senf import text2fsn, fsn2text, path2fsn, mkstemp, fsnative
  File "/builddir/build/BUILD/mutagen-1.42.0/mutagen/_senf/__init__.py", line 32, in <module>
    from ._stdlib import sep, pathsep, curdir, pardir, altsep, extsep, devnull, \
  File "/builddir/build/BUILD/mutagen-1.42.0/mutagen/_senf/_stdlib.py", line 28, in <module>
    from ._environ import environ
  File "/builddir/build/BUILD/mutagen-1.42.0/mutagen/_senf/_environ.py", line 133, in <module>
    class Environ(collections.MutableMapping):
AttributeError: module 'collections' has no attribute 'MutableMapping'


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

"The abstract base classes in collections.abc no longer are exposed in the regular collections module. This will help create a clearer distinction between the concrete classes and the abstract base classes."


For the build logs, see:
https://copr-be.cloud.fedoraproject.org/results/@python/python3.9/fedora-rawhide-x86_64/01149179-python-mutagen/

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

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.