flake8 2.2.1

the modular source code checker: pep8, pyflakes and co

Flake8 is a wrapper around these tools:

• PyFlakes

• pep8

• Ned Batchelder’s McCabe script

Flake8 runs all the tools by launching the single flake8 script. It displays the warnings in a per-file, merged output.

It also adds a few features:

• files that contain this line are skipped:

  # flake8: noqa

• lines that contain a # noqa comment at the end will not issue warnings.

• a Git and a Mercurial hook.

• a McCabe complexity checker.

• extendable through flake8.extension entry points.

QuickStart

pip install flake8

To run flake8 just invoke it against any directory or Python module:

$ flake8 coolproject
coolproject/mod.py:97:1: F401 'shutil' imported but unused
coolproject/mod.py:625:17: E225 missing whitespace around operato
coolproject/mod.py:729:1: F811 redefinition of function 'readlines' from line 723
coolproject/mod.py:1028:1: F841 local variable 'errors' is assigned to but never used

The outputs of PyFlakes and pep8 (and the optional plugins) are merged and returned.

flake8 offers an extra option: –max-complexity, which will emit a warning if the McCabe complexity of a function is higher than the value. By default it’s deactivated:

$ flake8 --max-complexity 12 coolproject
coolproject/mod.py:97:1: F401 'shutil' imported but unused
coolproject/mod.py:625:17: E225 missing whitespace around operator
coolproject/mod.py:729:1: F811 redefinition of unused 'readlines' from line 723
coolproject/mod.py:939:1: C901 'Checker.check_all' is too complex (12)
coolproject/mod.py:1028:1: F841 local variable 'errors' is assigned to but never used
coolproject/mod.py:1204:1: C901 'selftest' is too complex (14)

This feature is quite useful to detect over-complex code. According to McCabe, anything that goes beyond 10 is too complex. See https://en.wikipedia.org/wiki/Cyclomatic_complexity.

Questions or Feedback

If you have questions you’d like to ask the developers, or feedback you’d like to provide, feel free to use the mailing list: [e-mail] We would love to hear from you. Additionally, if you have a feature you’d like to suggest, the mailing list would be the best place for it.

Links

• flake8 documentation

• pep8 documentation

CHANGES

2.2.1 - 2014-06-30

• Turn off multiple jobs by default. To enable automatic use of all CPUs, use --jobs=auto. Fixes #155 and #154.

2.2.0 - 2014-06-22

• New option doctests to run Pyflakes checks on doctests too

• New option jobs to launch multiple jobs in parallel

• Turn on using multiple jobs by default using the CPU count

• Add support for python -m flake8 on Python 2.7 and Python 3

• Fix Git and Mercurial hooks: issues #88, #133, #148 and #149

• Fix crashes with Python 3.4 by upgrading dependencies

• Fix traceback when running tests with Python 2.6

• Fix the setuptools command python setup.py flake8 to read the project configuration

2.1.0 - 2013-10-26

• Add FLAKE8_LAZY and FLAKE8_IGNORE environment variable support to git and mercurial hooks

• Force git and mercurial hooks to repsect configuration in setup.cfg

• Only check staged files if that is specified

• Fix hook file permissions

• Fix the git hook on python 3

• Ignore non-python files when running the git hook

• Ignore .tox directories by default

• Flake8 now reports the column number for PyFlakes messages

2.0.0 - 2013-02-23

• Pyflakes errors are prefixed by an F instead of an E

• McCabe complexity warnings are prefixed by a C instead of a W

• Flake8 supports extensions through entry points

• Due to the above support, we require setuptools

• We publish the documentation

• Fixes #13: pep8, pyflakes and mccabe become external dependencies

• Split run.py into main.py, engine.py and hooks.py for better logic

• Expose our parser for our users

• New feature: Install git and hg hooks automagically

• By relying on pyflakes (0.6.1), we also fixed #45 and #35

1.7.0 - 2012-12-21

• Fixes part of #35: Exception for no WITHITEM being an attribute of Checker for Python 3.3

• Support stdin

• Incorporate @phd’s builtins pull request

• Fix the git hook

• Update pep8.py to the latest version

1.6.2 - 2012-11-25

• fixed the NameError: global name ‘message’ is not defined (#46)

1.6.1 - 2012-11-24

• fixed the mercurial hook, a change from a previous patch was not properly applied

• fixed an assumption about warnings/error messages that caused an exception to be thrown when McCabe is used

1.6 - 2012-11-16

• changed the signatures of the check_file function in flake8/run.py, skip_warning in flake8/util.py and the check, checkPath functions in flake8/pyflakes.py.

• fix --exclude and --ignore command flags (#14, #19)

• fix the git hook that wasn’t catching files not already added to the index (#29)

• pre-emptively includes the addition to pep8 to ignore certain lines. Add # nopep8 to the end of a line to ignore it. (#37)

• check_file can now be used without any special prior setup (#21)

• unpacking exceptions will no longer cause an exception (#20)

• fixed crash on non-existent file (#38)

1.5 - 2012-10-13

• fixed the stdin

• make sure mccabe catches the syntax errors as warnings

• pep8 upgrade

• added max_line_length default value

• added Flake8Command and entry points if setuptools is around

• using the setuptools console wrapper when available

1.4 - 2012-07-12

• git_hook: Only check staged changes for compliance

• use pep8 1.2

1.3.1 - 2012-05-19

• fixed support for Python 2.5

1.3 - 2012-03-12

• fixed false W402 warning on exception blocks.

1.2 - 2012-02-12

• added a git hook

• now Python 3 compatible

• mccabe and pyflakes have warning codes like pep8 now

1.1 - 2012-02-14

• fixed the value returned by –version

• allow the flake8: header to be more generic

• fixed the “hg hook raises ‘physical lines’” bug

• allow three argument form of raise

• now uses setuptools if available, for ‘develop’ command

1.0 - 2011-11-29

• Deactivates by default the complexity checker

• Introduces the complexity option in the HG hook and the command line.

0.9 - 2011-11-09

• update pep8 version to 0.6.1

• mccabe check: gracefully handle compile failure

0.8 - 2011-02-27

• fixed hg hook

• discard unexisting files on hook check

0.7 - 2010-02-18

• Fix pep8 initialization when run through Hg

• Make pep8 short options work when run through the command line

• Skip duplicates when controlling files via Hg

0.6 - 2010-02-15

• Fix the McCabe metric on some loops