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pytest plugin to run the mccabe code complexity checker.

Project description


pytest plugin for checking cyclomatic complexity of python source with mccabe.

NOTE: I (@The-Compiler) stopped using this plugin in 2016. While I will still review pull requests and release new versions if needed by the community, I do not have the time to continue maintaining this plugin myself. You might want to consider switching to pytest-flake8 or tox + flake8 instead (see some arguments on why).


install via:

pip install pytest-mccabe

if you then type:

pytest --mccabe

every file ending in .py will be discovered and run through mccabe, starting from the command line arguments.

Simple usage example

Consider you have this (deliberately bad and complex) code:


import random
import os.path

def some_function():
    num = random.random()
    if 0 <= num < 0.1:
    elif 0.1 <= num < 0.2:
    elif 0.2 <= num < 0.3:
    elif 0.3 <= num < 0.4:
    elif 0.4 <= num < 0.5:
    elif 0.5 <= num < 0.6:
    elif 0.6 <= num < 0.7:
    elif 0.7 <= num < 0.8:
    elif 0.8 <= num < 0.9:
    elif 0.9 <= num < 1:

Running pytest with pytest-mccabe installed shows you this function is considered too complex:

$ pytest -q --mccabe
============================== FAILURES ==============================
____________________________ mccabe-check ____________________________
.../ C901 'some_function' is too complex (11)

Configuring mccabe complexity per project and file

You may configure the maximum complexity for your project by adding an mccabe-complexity entry to pytest config file (e.g. setup.cfg) like this:


Rerunning with the above example will now look better:

$ pytest -q --mccabe
1 passed in 0.00 seconds

If you have some files where you want to set a higher complexity than the project-wide one, you can start a mccabe-complexity line with a glob-pattern:

mccabe-complexity =
    *.py 7 10

Ignoring certain functions

You can exclude certain functions from the complexity check by adding comments like this:

def some_function():  # noqa

def another_function():  # pragma: no mccabe

(both will work - # noqa is mainly there for flake8 compatibility)

Running mccabe checks and no other tests

You can restrict your test run to only perform “mccabe” tests and not any other tests by typing:

pytest --mccabe -m mccabe

This will only run tests that are marked with the “mccabe” keyword which is added for the mccabe test items added by this plugin.

If you are using pytest < 2.4, then use the following invocation to the same effect:

pytest --mccabe -k mccabe


The repository of this plugin is at

For more info on pytest see

The code is based on Florian Schulze’s excellent pytest-flakes - Thanks!



  • Initial release.


  • Drop support for Python 2.6, 3.2, 3.3 and 3.4

  • Add support for Python 3.5, 3.6 and 3.7

  • Make this plugin compatible with pytest 4.x and 5.x

  • Drop support for “ test”

  • Remove outdated pytest-cache dependency

  • Various code/CI cleanups


  • Drop support for Python 2.7

  • Drop support for pytest < 5.4

  • Add support for Python 3.8 (no changes required)

  • Fix deprecation warnings with pytest >= 5.4 (thanks to Martin Thoma for the PR!)

  • Various code/CI cleanups

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