# flake8-bugbear > A plugin for flake8 finding likely bugs and design problems in your program. Contains warnings that don't belong in pyflakes and pycodestyle. - **URL**: https://www.freshcrate.ai/projects/flake8-bugbear - **Author**: pypi - **Category**: Frameworks - **Latest version**: `main@2026-05-29` (2026-05-29) - **License**: MIT - **Source**: https://github.com/PyCQA/flake8-bugbear#change-log - **Homepage**: https://pypi.org/project/flake8-bugbear/ - **Language**: Python - **GitHub**: 1,115 stars, 115 forks - **Registry**: pypi (`flake8-bugbear`) - **Tags**: `bugbear`, `bugs`, `flake8`, `linter`, `pyflakes`, `pylint`, `pypi`, `qa` ## Description ============== flake8-bugbear ============== .. image:: https://github.com/PyCQA/flake8-bugbear/actions/workflows/ci.yml/badge.svg :target: https://github.com/PyCQA/flake8-bugbear/actions/workflows/ci.yml .. image:: https://img.shields.io/badge/code%20style-black-000000.svg :target: https://github.com/psf/black .. image:: https://results.pre-commit.ci/badge/github/PyCQA/flake8-bugbear/main.svg :target: https://results.pre-commit.ci/latest/github/PyCQA/flake8-bugbear/main :alt: pre-commit.ci status A plugin for ``flake8`` finding likely bugs and design problems in your program. Contains warnings that don't belong in ``pyflakes`` and ``pycodestyle``:: bug·bear (bŭg′bâr′) n. 1. A cause of fear, anxiety, or irritation: *Overcrowding is often a bugbear for train commuters.* 2. A difficult or persistent problem: *"One of the major bugbears of traditional AI is the difficulty of programming computers to recognize that different but similar objects are instances of the same type of thing" (Jack Copeland).* 3. A fearsome imaginary creature, especially one evoked to frighten children. It is felt that these lints don't belong in the main Python tools as they are very opinionated and do not have a PEP or standard behind them. Due to ``flake8`` being designed to be extensible, the original creators of these lints believed that a plugin was the best route. This has resulted in better development velocity for contributors and adaptive deployment for ``flake8`` users. Installation ------------ Install from ``pip`` with: .. code-block:: sh pip install flake8-bugbear It will then automatically be run as part of ``flake8``; you can check it has been picked up with: .. code-block:: sh $ flake8 --version 3.5.0 (assertive: 1.0.1, flake8-bugbear: 18.2.0, flake8-comprehensions: 1.4.1, mccabe: 0.6.1, pycodestyle: 2.3.1, pyflakes: 1.6.0) CPython 3.7.0 on Darwin Development ----------- If you'd like to do a PR we have development instructions `here `_. List of warnings ---------------- .. _B001: **B001**: Do not use bare ``except:``, it also catches unexpected events like memory errors, interrupts, system exit, and so on. Prefer ``except Exception:``. If you're sure what you're doing, be explicit and write ``except BaseException:``. Disable ``E722`` to avoid duplicate warnings. .. _B002: **B002**: Python does not support the unary prefix increment. Writing ``++n`` is equivalent to ``+(+(n))``, which equals ``n``. You meant ``n += 1``. .. _B003: **B003**: Assigning to ``os.environ`` doesn't clear the environment. Subprocesses are going to see outdated variables, in disagreement with the current process. Use ``os.environ.clear()`` or the ``env=`` argument to Popen. .. _B004: **B004**: Using ``hasattr(x, '__call__')`` to test if ``x`` is callable is unreliable. If ``x`` implements custom ``__getattr__`` or its ``__call__`` is itself not callable, you might get misleading results. Use ``callable(x)`` for consistent results. .. _B005: **B005**: Using ``.strip()`` with multi-character strings is misleading the reader. It looks like stripping a substring. Move your character set to a constant if this is deliberate. Use ``.replace()``, ``.removeprefix()``, ``.removesuffix()`` or regular expressions to remove string fragments. .. _B006: **B006**: Do not use mutable data structures for argument defaults. They are created during function definition time. All calls to the function reuse this one instance of that data structure, persisting changes between them. .. _B007: **B007**: Loop control variable not used within the loop body. If this is intended, start the name with an underscore. .. _B008: **B008**: Do not perform function calls in argument defaults. The call is performed only once at function definition time. All calls to your function will reuse the result of that definition-time function call. If this is intended, assign the function call to a module-level variable and use that variable as a default value. .. _B009: **B009**: Do not call ``getattr(x, 'attr')``, instead use normal property access: ``x.attr``. Missing a default to ``getattr`` will cause an ``AttributeError`` to be raised for non-existent properties. There is no additional safety in using ``getattr`` if you know the attribute name ahead of time. .. _B010: **B010**: Do not call ``setattr(x, 'attr', val)``, instead use normal property access: ``x.attr = val``. There is no additional safety in using ``setattr`` if you know the attribute name ahead of time. .. _B011: **B011**: Do not call ``assert False`` since ``python -O`` removes these calls. Instead callers should ``raise AssertionError()``. .. _B012: **B012**: Use of ``break``, ``continue`` or ``return`` inside ``finally`` blocks will silence exceptions or override return values from the ``try`` or ``except`` blocks. To s ## Recent releases | Version | Date | Urgency | Changes | | --- | --- | --- | --- | | `main@2026-05-29` | 2026-05-29 | High | Latest activity on main branch | | `25.11.29` | 2026-04-21 | Low | Imported from PyPI (25.11.29) | | `main@2026-03-16` | 2026-03-16 | Low | Latest activity on main branch | | `main@2026-03-16` | 2026-03-16 | Low | Latest activity on main branch | | `main@2026-03-16` | 2026-03-16 | Low | Latest activity on main branch | | `25.10.21` | 2025-10-22 | Low | * B042: New check for reminding to call super().__init__ in custom exceptions * B028: Skip if skip_file_prefixes is used (#503) * B912: New check for `map()` without an explicit `strict=` parameter. (#516) * Add python3.14 Support / CI * Remove python3.9 support / CI * flake8-bugbear now requires at least Python 3.10, like the next release of flake8 | | `24.12.12` | 2024-12-12 | Low | * B012 and B025 now also handle try/except* (#500) * Skip B028 if warnings.warn is called with ``*args`` or ``**kwargs`` (#501) * Add B911: itertools.batched without strict= (#502) * Readme has anchors per check (they do not seem to render on GitHub tho) | | `24.10.31` | 2024-10-31 | Low | * B041: New dictionary same key AND value check (#496) * B037: Fix typo in error message * B024: No longer treats assigned class variables as abstract (#471) * Bump required attrs version to 22.2.0 | | `24.8.19` | 2024-08-20 | Low | * B910: implement to suggest using Counter() instead of defaultdict(int) (#489) * B901: Do not trigger with explicit Generator return type (#481) * B008: add some comments, rename b008_extend_immutable_calls (#476) * B040: exception with note added not reraised or used (#477) * B039, Add ``ContextVar`` with mutable literal or function call as default * B040: Add Exception with added note not reraised. (#474) * Run tests in Python 3.13 * Type annotated code (#481 + #483) * Replace hash wi | | `24.4.26` | 2024-04-26 | Low | * B909: Fix false positive affecting containers of mutables (#469) | ## Citation - HTML: https://www.freshcrate.ai/projects/flake8-bugbear - Markdown: https://www.freshcrate.ai/projects/flake8-bugbear.md - Dependencies JSON: https://www.freshcrate.ai/api/projects/flake8-bugbear/deps _Generated by freshcrate.ai. Indexes pypi releases for AI-agent ecosystem packages._