IndexError with Unicode double border character

[Hugo van Kemenade]

how did you install flake8?

$ pip install flake8
Requirement already satisfied: flake8 in /Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages (7.1.0)
Requirement already satisfied: mccabe<0.8.0,>=0.7.0 in /Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages (from flake8) (0.7.0)
Requirement already satisfied: pycodestyle<2.13.0,>=2.12.0 in /Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages (from flake8) (2.12.0)
Requirement already satisfied: pyflakes<3.3.0,>=3.2.0 in /Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages (from flake8) (3.2.0)

unmodified output of flake8 --bug-report

{
  "platform": {
    "python_implementation": "CPython",
    "python_version": "3.12.4",
    "system": "Darwin"
  },
  "plugins": [
    {
      "plugin": "mccabe",
      "version": "0.7.0"
    },
    {
      "plugin": "pycodestyle",
      "version": "2.12.0"
    },
    {
      "plugin": "pyflakes",
      "version": "3.2.0"
    }
  ],
  "version": "7.1.0"
}

describe the problem

what I expected to happen

No IndexError, flake8 to report any style issues found.

sample code

assert ("""
    ╝""".strip()
)

Minimal reproducer from this full test case: https://github.com/jazzband/prettytable/blob/f044b0e2c99680c975e5d4523771f819934f4611/tests/test_prettytable.py#L1205-L1222

Also a problem with other double border characters, works okay replacing it with some ASCII thing like "a".

No problem if removing the .strip(), or running Black which removes the wrapping parentheses:

assert """
    ╝""".strip()

commands ran

$ ❯ flake8 t.py
Found existing alias for "flake8". You should use: "f8"
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.12/bin/flake8", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/flake8/main/cli.py", line 23, in main
    app.run(argv)
  File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/flake8/main/application.py", line 198, in run
    self._run(argv)
  File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/flake8/main/application.py", line 187, in _run
    self.run_checks()
  File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/flake8/main/application.py", line 103, in run_checks
    self.file_checker_manager.run()
  File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/flake8/checker.py", line 238, in run
    self.run_serial()
  File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/flake8/checker.py", line 221, in run_serial
    ).run_checks()
      ^^^^^^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/flake8/checker.py", line 527, in run_checks
    self.process_tokens()
  File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/flake8/checker.py", line 512, in process_tokens
    self.handle_newline(token_type)
  File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/flake8/checker.py", line 542, in handle_newline
    self.run_logical_checks()
  File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/flake8/checker.py", line 439, in run_logical_checks
    comments, logical_line, mapping = self.processor.build_logical_line()
                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/flake8/processor.py", line 231, in build_logical_line
    comments, logical, mapping_list = self.build_logical_line_tokens()
                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/site-packages/flake8/processor.py", line 212, in build_logical_line_tokens
    previous_text = self.lines[row_index][column_index]
                    ~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^
IndexError: string index out of range

[Anthony Sottile]

this is a bug in cpython 3.12.4 and will be fixed in 3.12.5

[Hugo van Kemenade]

Thank you, confirmed fixed with the latest 3.12 branch.