Python 3.14: TypeError: HelpFormatter.__init__() got an unexpected keyword argument 'prefix_chars' #3523
Description
Issue
With Python 3.14.0b1, tox immediately fails to start with TypeError: HelpFormatter.__init__() got an unexpected keyword argument 'prefix_chars', because it overrides HelpFormatter in an incompatible way.
This is due to:
See also:
- Fix HelpFormatter for Python 3.14 pypa/virtualenv#2878
- Fix argparse for Python 3.14 python/mypy#19020
Environment
Provide at least:
- OS: Archlinux, Python 3.14.0b1
Output of pip list of the host Python, where tox is installed
cachetools 5.5.2 chardet 5.2.0 colorama 0.4.6 distlib 0.3.9 filelock 3.18.0 packaging 25.0 pip 25.1.1 platformdirs 4.3.8 pluggy 1.5.0 pyproject-api 1.9.0 tox 4.25.1.dev6+g4a8e50e2 /home/florian/tmp/tox virtualenv 20.31.1Output of running tox
Output of tox -rvv
Traceback (most recent call last): File "<frozen runpy>", line 198, in _run_module_as_main File "<frozen runpy>", line 88, in _run_code File "/home/florian/tmp/tox/src/tox/__main__.py", line 6, in <module> run() ~~~^^ File "/home/florian/tmp/tox/src/tox/run.py", line 20, in run result = main(sys.argv[1:] if args is None else args) File "/home/florian/tmp/tox/src/tox/run.py", line 39, in main state = setup_state(args) File "/home/florian/tmp/tox/src/tox/run.py", line 53, in setup_state options = get_options(*args) File "/home/florian/tmp/tox/src/tox/config/cli/parse.py", line 39, in get_options parsed, cmd_handlers = _get_all(args) ~~~~~~~~^^^^^^ File "/home/florian/tmp/tox/src/tox/config/cli/parse.py", line 69, in _get_all tox_parser = _get_parser() File "/home/florian/tmp/tox/src/tox/config/cli/parse.py", line 76, in _get_parser tox_parser = ToxParser.core() # load the core options File "/home/florian/tmp/tox/src/tox/config/cli/parser.py", line 300, in core return cls( prog=NAME, ...<3 lines>... description="create and set up environments to run command(s) in them", ) File "/home/florian/tmp/tox/src/tox/config/cli/parser.py", line 149, in __init__ super().__init__(*args, **kwargs) ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^ File "/home/florian/tmp/tox/src/tox/config/cli/parser.py", line 39, in __init__ super().__init__(*args, **kwargs) ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^ File "/usr/lib/python3.14/argparse.py", line 1920, in __init__ self.add_argument( ~~~~~~~~~~~~~~~~~^ default_prefix+'h', default_prefix*2+'help', ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ action='help', default=SUPPRESS, ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help=_('show this help message and exit')) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/home/florian/tmp/tox/src/tox/config/cli/parser.py", line 284, in add_argument result = super().add_argument(*args, **kwargs) File "/usr/lib/python3.14/argparse.py", line 1562, in add_argument formatter = self._get_formatter() File "/usr/lib/python3.14/argparse.py", line 2729, in _get_formatter return self.formatter_class( ~~~~~~~~~~~~~~~~~~~~^ prog=self.prog, ^^^^^^^^^^^^^^^ prefix_chars=self.prefix_chars, ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ color=self.color, ^^^^^^^^^^^^^^^^^ ) ^ TypeError: HelpFormatter.__init__() got an unexpected keyword argument 'prefix_chars'