McCabe complexity checker

Ned's script to check McCabe complexity.

This module provides a plugin for flake8, the Python code checker.

Installation

You can install, upgrade, or uninstall mccabe with these commands:

$ pip install mccabe
$ pip install --upgrade mccabe
$ pip uninstall mccabe

Standalone script

The complexity checker can be used directly:

$ python -m mccabe --min 5 mccabe.py
("185:1: 'PathGraphingAstVisitor.visitIf'", 5)
("71:1: 'PathGraph.to_dot'", 5)
("245:1: 'McCabeChecker.run'", 5)
("283:1: 'main'", 7)
("203:1: 'PathGraphingAstVisitor.visitTryExcept'", 5)
("257:1: 'get_code_complexity'", 5)

Plugin for Flake8

When both flake8 2+ and mccabe are installed, the plugin is available in flake8:

$ flake8 --version
2.0 (pep8: 1.4.2, pyflakes: 0.6.1, mccabe: 0.2)

By default the plugin is disabled. Use the --max-complexity switch to enable it. It will emit a warning if the McCabe complexity of a function is higher than the provided value:

$ flake8 --max-complexity 10 coolproject
...
coolproject/mod.py:1204:1: C901 'CoolFactory.prepare' is too complex (14)

This feature is quite useful for detecting over-complex code. According to McCabe, anything that goes beyond 10 is too complex.

Flake8 has many features that mccabe does not provide. Flake8 allows users to ignore violations reported by plugins with # noqa. Read more about this in their documentation. To silence violations reported by mccabe, place your # noqa: C901 on the function definition line, where the error is reported for (possibly a decorator).

Links

• Feedback and ideas: http://mail.python.org/mailman/listinfo/code-quality
• Cyclomatic complexity: http://en.wikipedia.org/wiki/Cyclomatic_complexity
• Ned Batchelder's script: http://nedbatchelder.com/blog/200803/python_code_complexity_microtool.html
• McCabe complexity: http://en.wikipedia.org/wiki/Cyclomatic_complexity

Changes

0.7.0 - 2021-01-23

• Drop support for all versions of Python lower than 3.6
• Add support for Python 3.8, 3.9, and 3.10
• Fix option declaration for Flake8

0.6.1 - 2017-01-26

• Fix signature for PathGraphingAstVisitor.default to match the signature for ASTVisitor

0.6.0 - 2017-01-23

• Add support for Python 3.6
• Fix handling for missing statement types

0.5.3 - 2016-12-14

• Report actual column number of violation instead of the start of the line

0.5.2 - 2016-07-31

• When opening files ourselves, make sure we always name the file variable

0.5.1 - 2016-07-28

• Set default maximum complexity to -1 on the class itself

0.5.0 - 2016-05-30

• PyCon 2016 PDX release
• Add support for Flake8 3.0

0.4.0 - 2016-01-27

• Stop testing on Python 3.2
• Add support for async/await keywords on Python 3.5 from PEP 0492

0.3.1 - 2015-06-14

• Include test_mccabe.py in releases.
• Always coerce the max_complexity value from Flake8's entry-point to an integer.

0.3 - 2014-12-17

• Computation was wrong: the mccabe complexity starts at 1, not 2.
• The max-complexity value is now inclusive. E.g.: if the value is 10 and the reported complexity is 10, then it passes.
• Add tests.

0.2.1 - 2013-04-03

• Do not require setuptools in setup.py. It works around an issue with pip and Python 3.

0.2 - 2013-02-22

• Rename project to mccabe.
• Provide flake8.extension setuptools entry point.
• Read max-complexity from the configuration file.
• Rename argument min_complexity to threshold.

0.1 - 2013-02-11

• First release