A plugin for flake8 finding likely bugs and design problems in your program. Contains warnings that don't belong in pyflakes and pycodestyle.
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.
List of warnings
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:.
B002: Python does not support the unary prefix increment. Writing ++n is equivalent to +(+(n)), which equals n. You meant n += 1.
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 Subprocesses are going to see outdated variables, in disagreement with the current process.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: 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.
Python 3 compatibility warnings
These have higher risk of false positives but discover regressions that are dangerous to slip through when test coverage is not great. Let me know if a popular library is triggering any of the following warnings for valid code.
B301: Python 3 does not include .iter* methods on dictionaries. The default behavior is to return iterables. Simply remove the iter prefix from the method. For Python 2 compatibility, also prefer the Python 3 equivalent if you expect that the size of the dict to be small and bounded. The performance regression on Python 2 will be negligible and the code is going to be the clearest. Alternatively, use six.iter* or future.utils.iter*.
B302: Python 3 does not include .view* methods on dictionaries. The default behavior is to return viewables. Simply remove the view prefix from the method. For Python 2 compatibility, also prefer the Python 3 equivalent if you expect that the size of the dict to be small and bounded. The performance regression on Python 2 will be negligible and the code is going to be the clearest. Alternatively, use six.view* or future.utils.view*.
B303: The __metaclass__ attribute on a class definition does nothing on Python 3. Use class MyClass(BaseClass, metaclass=...). For Python 2 compatibility, use six.add_metaclass.
B304: sys.maxint is not a thing on Python 3. Use sys.maxsize.
B305: .next() is not a thing on Python 3. Use the next() builtin. For Python 2 compatibility, use six.next().
B306: BaseException.message has been deprecated as of Python 2.6 and is removed in Python 3. Use str(e) to access the user-readable message. Use e.args to access arguments passed to the exception.
The following warnings are disabled by default because they are controversial. They may or may not apply to you, enable them explicitly in your configuration if you find them useful.
To enable these checks, specify a --select command-line option or select= option in your config file. As of Flake8 3.0, this option is a whitelist (checks not listed are being implicitly disabled), so you have to explicitly specify all checks you want enabled. For example:
[flake8] max-line-length = 80 max-complexity = 12 ... select = C,E,F,W,B,B901
Note that we’re enabling the complexity checks, the PEP8 pycodestyle errors and warnings, the pyflakes fatals and all default Bugbear checks. Finally, we’re also specifying B901 as a check that we want enabled. If you’d like all optional warnings to be enabled for you (future proof your config!), say B9 instead of B901.
B901: Using return x in a generator function used to be syntactically invalid in Python 2. In Python 3 return x can be used in a generator as a return value in conjunction with yield from. Users coming from Python 2 may expect the old behavior which might lead to bugs. Use native async def coroutines or mark intentional return x usage with # noqa on the same line.
python setup.py test
OMG, this is Python 3 only!
Relax, you can run flake8 with all popular plugins as a tool perfectly fine under Python 3.5+ even if you want to analyze Python 2 code. This way you’ll be able to parse all of the new syntax supported on Python 3 but also effectively all the Python 2 syntax at the same time.
By making the code exclusively Python 3.5+, I’m able to focus on the quality of the checks and re-use all the nice features of the new releases (check out pathlib) instead of wasting cycles on Unicode compatiblity, etc.
- bugfix: don’t raise false positives in B901 on closures within generators
- introduced B004
- introduced B901, thanks Markus!
- update flake8 constraint to at least 3.0.0
- introduced B003
- bugfix: don’t omit message code in B306’s warning
- change dependency on pep8 to dependency on pycodestyle, update flake8 constraint to at least 2.6.2
- introduced B306
- bugfix: don’t crash on files with tuple unpacking in class bodies
- introduced B002, B301, B302, B303, B304, and B305
- packaging herp derp
- bugfix: include tests in the source package (to make setup.py test work for everyone)
- bugfix: explicitly open README.rst in UTF-8 in setup.py for systems with other default encodings
- first published version