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 <http://flake8.pycqa.org/en/latest/user/violations.html#in-line-ignoring-errors>__.
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

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mccabe

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