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

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