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PyCQA/mccabe

A Python tool that computes McCabe cyclomatic complexity for functions and runs as a flake8 plugin to flag overly complex code.

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What is it?

mccabe measures the McCabe (cyclomatic) complexity of Python code, a count of the independent execution paths through a function. High scores point to functions that are hard to read and test. The project can be run as a standalone module on a file, printing each function with its complexity above a chosen threshold.

It also works as a plugin for flake8, the Python code checker. Once installed, the plugin is disabled by default and is enabled with the --max-complexity option, which reports a C901 warning for any function whose complexity exceeds the given value.

The project is maintained under the PyCQA organization and supports recent Python 3 versions, with the 0.7.0 release dropping support for Python versions below 3.6.

Key features

  • 01Computes McCabe cyclomatic complexity for Python functions and methods.
  • 02Runs as a standalone command via python -m mccabe with a --min threshold.
  • 03Integrates with flake8 through the --max-complexity option and reports C901 warnings.
  • 04Supports async/await syntax and recent Python 3 versions.

Use cases

  • Flagging overly complex functions during code review or in continuous integration.
  • Enforcing a complexity limit across a Python project through flake8 configuration.
  • Finding the most complex functions in a module before refactoring.

Quick start

  1. 1

    Install mccabe from PyPI with pip

    pip install mccabe
  2. 2

    Run the standalone checker on a Python file to list the most complex functions

    python -m mccabe --min 5 mccabe.py
  3. 3

    Use it as a flake8 plugin by setting a maximum complexity

    flake8 --max-complexity 10 coolproject

Things to know

  • The license is not clearly declared in the project metadata, so check the license file before commercial use.
  • Plugin checks are disabled by default and must be enabled with --max-complexity.

In collections

Code linters & formatters

Topics

#python#code-quality#cyclomatic-complexity#flake8#linter#static-analysis#complexity#complexity-analysis#flake8-extensions#flake8-plugin

FAQ

What is mccabe?
A Python tool that computes McCabe cyclomatic complexity for functions and runs as a flake8 plugin to flag overly complex code. mccabe measures the McCabe (cyclomatic) complexity of Python code, a count of the independent execution paths through a function. High scores point to functions that are hard to read and test. The project can be run as a standalone module on a file, printing each function with its complexity above a chosen threshold.
Is mccabe free to use? What license does it have?
mccabe is open source under the Other license. Check the license terms before using it in commercial products.
Is mccabe still maintained?
Actively maintained. The last commit to mccabe was on Oct 12, 2026.
What can I use mccabe for?
Flagging overly complex functions during code review or in continuous integration. Enforcing a complexity limit across a Python project through flake8 configuration. Finding the most complex functions in a module before refactoring.
How do I install mccabe?
Install mccabe from PyPI with pip: pip install mccabe Run the standalone checker on a Python file to list the most complex functions: python -m mccabe --min 5 mccabe.py Use it as a flake8 plugin by setting a maximum complexity: flake8 --max-complexity 10 coolproject
Where can I get mccabe?
The source code and installation instructions are on GitHub: https://github.com/PyCQA/mccabe

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