Flake8 is a wrapper around these tools:
- 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.
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.