Hello,
after the last distribution-update this days mitmproxy doesn't start:

mitmproxy
Traceback (most recent call last):
File "/usr/bin/mitmproxy", line 11, in <module>
load_entry_point('mitmproxy==5.1.1', 'console_scripts', 'mitmproxy')()
File "/usr/lib/python3/dist-packages/mitmproxy/tools/_main.py", line 147, in mitmproxy
run(console.master.ConsoleMaster, cmdline.mitmproxy, args)
File "/usr/lib/python3/dist-packages/mitmproxy/tools/_main.py", line 71, in run
opts = options.Options()
File "/usr/lib/python3/dist-packages/mitmproxy/options.py", line 50, in init
self.add_option(
File "/usr/lib/python3/dist-packages/mitmproxy/optmanager.py", line 109, in add_option
self._options[name] = _Option(name, typespec, default, help, choices)
File "/usr/lib/python3/dist-packages/mitmproxy/optmanager.py", line 34, in init
typecheck.check_option_type(name, default, typespec)
File "/usr/lib/python3/dist-packages/mitmproxy/utils/typecheck.py", line 73, in check_option_type
elif not isinstance(value, typeinfo):
File "/usr/lib/python3.9/typing.py", line 697, in instancecheck
return self.subclasscheck(type(obj))
File "/usr/lib/python3.9/typing.py", line 700, in subclasscheck
raise TypeError("Subscripted generics cannot be used with"
TypeError: Subscripted generics cannot be used with class and instance checks

This failure is described in github under "TypeError: Subscripted generics cannot be used with class and instance checks under python 3.9.0b1 0004021".

I believe, that mitmproxy mustb be fixed for python 3.9.0b1

Bye
Rose