ruff/docs/rules/function-is-too-complex.md

function-is-too-complex (C901)

Derived from the mccabe linter.

What it does

Checks for functions with a high McCabe complexity.

The McCabe complexity of a function is a measure of the complexity of the control flow graph of the function. It is calculated by adding one to the number of decision points in the function. A decision point is a place in the code where the program has a choice of two or more paths to follow.

Why is this bad?

Functions with a high complexity are hard to understand and maintain.

Example

def foo(a, b, c):
    if a:
        if b:
            if c:
                return 1
            else:
                return 2
        else:
            return 3
    else:
        return 4

Use instead:

def foo(a, b, c):
    if not a:
        return 4
    if not b:
        return 3
    if not c:
        return 2
    return 1