Flake8

7.3.0 · active · verified Sat Mar 28

Flake8 is a modular source code checker that wraps PyFlakes, pycodestyle, and Ned Batchelder's McCabe script. It runs all these tools with a single command, displaying a merged output of warnings. As of version 7.3.0, it is actively maintained with releases as necessary, often driven by bug fixes and new features.

Warnings

breaking Flake8 7.0.0 removed the `--include-in-doctest` and `--exclude-from-doctest` options.
Fix: Review your Flake8 configuration and remove these options if present. Adjust your exclusion patterns using `--exclude` or `exclude` in your config file if you previously relied on doctest-specific exclusions.
breaking Flake8 6.0.0 removed the `--diff` option. It also became stricter, producing errors for invalid codes specified in configuration files or if the file specified in `--extend-config` does not exist. Additionally, Python 3.8.1 or newer is now required.
Fix: Remove `--diff` from your CI/local scripts. Validate your `.flake8`, `setup.cfg`, or `tox.ini` files for correct error codes and ensure all `--extend-config` paths are valid. Upgrade your Python interpreter to at least 3.8.1.
breaking Major releases (e.g., 3.0, 4.0, 5.0, 6.0, 7.0) historically include large-scale refactoring, 'subtly breaking CLI changes,' and breaking changes to its plugin interface. Always review release notes for new major versions.
Fix: Before upgrading to a new major version, carefully read the official release notes and migration guides. Test your Flake8 configuration and any custom plugins in a separate environment.
gotcha Flake8's ability to correctly parse Python code is dependent on the Python version it's installed and run with. If you are checking code written with newer Python language features (e.g., Python 3.10's structural pattern matching), Flake8 needs to be installed on a Python 3.10 interpreter to understand those features.
Fix: Ensure Flake8 is installed and executed using the same Python version that your project code targets. For example, use `python3.10 -m pip install flake8` and then `python3.10 -m flake8 .`
gotcha Flake8 options can be specified on the command-line, or in configuration files (`.flake8`, `setup.cfg`, `tox.ini`). Command-line options always take precedence over configuration file settings. This can lead to unexpected behavior if not understood.
Fix: When troubleshooting unexpected Flake8 behavior, first check command-line arguments, then project configuration files (in order of `.flake8`, `setup.cfg`, `tox.ini`), and finally default settings. Ensure no command-line options are inadvertently overriding your desired configuration.
gotcha Using `# noqa` comments to ignore errors on a line or file (`# flake8: noqa`) can be convenient but may hide legitimate bugs or style violations, degrading code quality over time if overused.
Fix: Use `# noqa` sparingly and only for very specific, justified cases. Prefer to fix the underlying issue or configure Flake8's `ignore` or `per-file-ignores` options in a `.flake8` config file for project-wide exclusions, documenting the reason for the exclusion.

Install

pip install flake8 Install Flake8

Quickstart

To check all Python files in the current directory and its subdirectories. You can also run it via `python -m flake8 .` to ensure the correct Python environment is used.

flake8 .

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