samba fails to build with Python 3.9.0a3.

Traceback (most recent call last):
  File "/builddir/build/BUILD/samba-4.12.0rc1/third_party/waf/waflib/Scripting.py", line 159, in waf_entry_point
    run_commands()
  File "/builddir/build/BUILD/samba-4.12.0rc1/third_party/waf/waflib/Scripting.py", line 255, in run_commands
    ctx = run_command(cmd_name)
  File "/builddir/build/BUILD/samba-4.12.0rc1/third_party/waf/waflib/Scripting.py", line 239, in run_command
    ctx.execute()
  File "/builddir/build/BUILD/samba-4.12.0rc1/third_party/waf/waflib/Configure.py", line 159, in execute
    super(ConfigurationContext, self).execute()
  File "/builddir/build/BUILD/samba-4.12.0rc1/third_party/waf/waflib/Context.py", line 204, in execute
    self.recurse([os.path.dirname(g_module.root_path)])
  File "/builddir/build/BUILD/samba-4.12.0rc1/third_party/waf/waflib/Context.py", line 286, in recurse
    user_function(self)
  File "/builddir/build/BUILD/samba-4.12.0rc1/wscript", line 233, in configure
    conf.PROCESS_SEPARATE_RULE('system_mitkrb5')
  File "./buildtools/wafsamba/samba_utils.py", line 685, in PROCESS_SEPARATE_RULE
    function_code = node.read('rU', None)
  File "/builddir/build/BUILD/samba-4.12.0rc1/third_party/waf/waflib/Node.py", line 185, in read
    return Utils.readf(self.abspath(), flags, encoding)
  File "/builddir/build/BUILD/samba-4.12.0rc1/third_party/waf/waflib/Utils.py", line 237, in readf
    with open(fname, m) as f:
ValueError: invalid mode: 'rUb'

See https://docs.python.org/3.9/whatsnew/3.9.html#changes-in-the-python-api

"open(), io.open(), codecs.open() and fileinput.FileInput no longer accept 'U' (“universal newline”) in the file mode. This flag was deprecated since Python 3.3. In Python 3, the “universal newline” is used by default when a file is open in text mode. The newline parameter of open() controls how universal newlines works."



For the build logs, see:
https://copr-be.cloud.fedoraproject.org/results/@python/python3.9/fedora-rawhide-x86_64/01212731-samba/

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

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.