flake8-expression-complexity

An extension for flake8 that validates expression complexity.

Splits code into expression and scores each according to how much one is complicated. Fires an error on each expression more complex than theshold.

Default complexity is 7, can be configured via --max-expression-complexity option.

Since Django ORM queries can produce long and readable expressions, checker can skip them. To enable this behaviour, use --ignore-django-orm-queries-complexity option.

Installation

pip install flake8-expression-complexity

Requires Python 3.10 to 3.14.

Example

if (
    (user and user.is_authorized)
    and user.subscriptions.filter(start_date__lt=today, end_date__gt=today).exists()
    and (
        user.total_credits_added
        - Check.objects.filter(user=user).aggregate(Sum('price'))['check__sum']
    )
    and UserAction.objects.filter(user=user).last().datetime > today - datetime.timedelta(days=10)
):
    ...

Usage:

$ flake8 --max-expression-complexity=3 test.py
text.py:2:5: ECE001 Expression is too complex (7.0 > 3)

Error codes

Contributing

We would love you to contribute to our project. It's simple:

1. Create an issue with bug you found or proposal you have. Wait for approve from maintainer.
2. Create a pull request. Make sure all checks are green.
3. Fix review comments if any.
4. Be awesome.

Here are useful tips:

• This project uses uv for dependency management. Run make install to set up a local environment.
• You can run all checks and tests with make check. Please do it before CI does.
• Install the pre-commit hooks with uv run pre-commit install to catch issues before you commit.
• We use BestDoctor python styleguide.
• We respect Django CoC. Make soft, not bullshit.