Max Line Length in style guide ignored with python 3.14 when checking multiple files

[badguy99]

how did you install flake8?

Installed on demand from TOML requirements as part of uv run command launch

unmodified output of flake8 --bug-report

{
  "platform": {
    "python_implementation": "CPython",
    "python_version": "3.14.2",
    "system": "Linux"
  },
  "plugins": [
    {
      "plugin": "mccabe",
      "version": "0.7.0"
    },
    {
      "plugin": "pep8-naming",
      "version": "0.15.1"
    },
    {
      "plugin": "pycodestyle",
      "version": "2.14.0"
    },
    {
      "plugin": "pyflakes",
      "version": "3.4.0"
    }
  ],
  "version": "7.3.0"
}

describe the problem

what I expected to happen

when using flake8 programmatically it should be possible to check multiple files with the configured style guide. This works correctly with python3.12 but seems to be ignored when using python 3.14

set up style guide

Python 3.14.2 (main, Jan  9 2026, 09:06:43) [GCC 8.5.0 20210514 (Red Hat 8.5.0-28.0.1)] on linux
Type "help", "copyright", "credits" or "license" for more information.
Ctrl click to launch VS Code Native REPL
>>> from flake8.api import legacy as flake8
>>> ignore_list = []
>>> line_length = 88
>>> style_guide = flake8.get_style_guide(extend_ignore=ignore_list, max_line_length=line_length, color="never")
>>> style_guide.options
Namespace(verbose=0, output_file=None, append_config=[], config=None, isolated=False, enable_extensions=None, require_plugins=None, filenames=[], quiet=0, color='never', count=False, exclude=['.svn', 'CVS', '.bzr', '.hg', '.git', '__pycache__', '.tox', '.nox', '.eggs', '*.egg'], extend_exclude=[], filename=['*.py'], stdin_display_name='stdin', format='default', hang_closing=False, ignore=None, extend_ignore=[], per_file_ignores='', max_line_length=88, max_doc_length=None, indent_size=4, select=None, extend_select=None, disable_noqa=False, show_source=False, statistics=False, exit_zero=False, jobs=JobsArgument('auto'), tee=False, benchmark=False, bug_report=False, max_complexity=-1, ignore_names=['setUp', 'tearDown', 'setUpClass', 'tearDownClass', 'setUpModule', 'tearDownModule', 'asyncSetUp', 'asyncTearDown', 'setUpTestData', 'failureException', 'longMessage', 'maxDiff'], classmethod_decorators=['classmethod'], staticmethod_decorators=['staticmethod'], builtins=None, doctests=False, extended_default_ignore=['N818'], extended_default_select=['C90', 'N8', 'F', 'E', 'W'])

Check files ignores the set max_line_length when running with multiple files

>>> style_guide.check_files(['file1.py', 'file2.py'])
file1.py:65:80: E501 line too long (88 > 79 characters)
file1.py:66:80: E501 line too long (85 > 79 characters)
file2.py:17:80: E501 line too long (81 > 79 characters)
file2.py:18:80: E501 line too long (87 > 79 characters)
file2.py:19:80: E501 line too long (88 > 79 characters)
<flake8.api.legacy.Report object at 0x7f070003b4d0>

However running the files individually works ok, and then it is possible to run the two files in the same check correctly

>>> style_guide.check_files(['file1.py'])
<flake8.api.legacy.Report object at 0x7f06ffc50690>
>>> style_guide.check_files(['file2.py'])
<flake8.api.legacy.Report object at 0x7f06ffc507d0>
>>> 
>>> 
>>> style_guide.check_files(['file1.py', 'file2.py'])
<flake8.api.legacy.Report object at 0x7f07001223f0>

[sigmavirus24]

What happens when you run it from the CLI with verbose logging?

[badguy99]

It works from CLI

> flake8 -v  --max-line-length 88 file1.py file2.py 
flake8.checker            MainProcess    231 INFO     Making checkers
flake8.main.application   MainProcess    521 INFO     Finished running
flake8.main.application   MainProcess    521 INFO     Reporting errors
flake8.main.application   MainProcess    521 INFO     Found a total of 0 violations and reported 0

If I turn the verbosity up further, it looks like one file is on ForkServerPoolWorker-1 and the other file is on ForkServerPoolWorker-2

[sigmavirus24]

You can set the verbosity on the python code as well to try to indicate difference between the two behaviors

[badguy99]

Frustratingly trying to set verbosity in the style guide programmatically runs in to the same issue, where specifying more than one file in the check_files list ignores all the options, then if you check just a single item list it is fine, and then it is also fine if you go back to the same two file list...

> python
Python 3.14.2 (main, Jan  9 2026, 09:06:43) [GCC 8.5.0 20210514 (Red Hat 8.5.0-28.0.1)] on linux
Type "help", "copyright", "credits" or "license" for more information.
Ctrl click to launch VS Code Native REPL
>>> from flake8.api import legacy as flake8
>>> ignore_list = []
>>> line_length = 88
>>> verbose = 4
>>> style_guide = flake8.get_style_guide(extend_ignore=ignore_list, max_line_length=line_length, color="never", verbose=verbose)
>>> style_guide.options
Namespace(verbose=4, output_file=None, append_config=[], config=None, isolated=False, enable_extensions=None, require_plugins=None, filenames=[], quiet=0, color='never', count=False, exclude=['.svn', 'CVS', '.bzr', '.hg', '.git', '__pycache__', '.tox', '.nox', '.eggs', '*.egg'], extend_exclude=[], filename=['*.py'], stdin_display_name='stdin', format='default', hang_closing=False, ignore=None, extend_ignore=[], per_file_ignores='', max_line_length=88, max_doc_length=None, indent_size=4, select=None, extend_select=None, disable_noqa=False, show_source=False, statistics=False, exit_zero=False, jobs=JobsArgument('auto'), tee=False, benchmark=False, bug_report=False, max_complexity=-1, ignore_names=['setUp', 'tearDown', 'setUpClass', 'tearDownClass', 'setUpModule', 'tearDownModule', 'asyncSetUp', 'asyncTearDown', 'setUpTestData', 'failureException', 'longMessage', 'maxDiff'], classmethod_decorators=['classmethod'], staticmethod_decorators=['staticmethod'], builtins=None, doctests=False, extended_default_ignore=['N818'], extended_default_select=['C90', 'N8', 'F', 'E', 'W'])


>>> style_guide.check_files(['file1.py', 'file2.py'])
file1.py:40:80: E501 line too long (87 > 79 characters)
file1.py:62:80: E501 line too long (88 > 79 characters)
file2.py:38:80: E501 line too long (81 > 79 characters)
<flake8.api.legacy.Report object at 0x7f05319f74d0>
>>> 


>>> 
>>> style_guide.check_files(['file1.py'])
>>>     """Run pyflakes on the Python libraries.
>>>     """Run pycodestyle (formally known as pep8).
>>>     style = pycodestyle.StyleGuide(
bracket depth 1 seen, col 34, visual min = 0
...         quiet=False,
...         max_line_length=line_length,
...         ignore=ignore_list,
...     )
>>>         msg = (
<snip>
<flake8.api.legacy.Report object at 0x7f0531620690>
>>>