CQ005: ComplexityCheck

Overview

Property	Value
ID	CQ005
Name	ComplexityCheck
Group	code-quality
Severity	WARNING

Description

Checks code complexity using cyclomatic complexity metrics.

High complexity indicates code that is:

Difficult to understand
Hard to test thoroughly
More likely to contain bugs
Expensive to maintain

What it checks

The check analyzes cyclomatic complexity and:

PASSED: All functions below complexity threshold (default 10)
FAILED: Functions exceed complexity threshold (lists them)
NOT_APPLICABLE: No complexity checker available

Cyclomatic complexity measures the number of independent paths through code. A function with:

1-5: Simple, easy to test
6-10: Moderate, consider refactoring
11-20: Complex, should refactor
21+: Very complex, must refactor

How to fix

Using ruff (recommended)

Ruff includes complexity checking. Enable it in pyproject.toml:

[tool.ruff.lint]
select = ["C901"]  # McCabe complexity

[tool.ruff.lint.mccabe]
max-complexity = 10

Run to see complex functions:

ruff check --select=C901 .

Using radon

Install and run radon:

pip install radon
radon cc src/my_package -a -s

Using flake8

pip install flake8
flake8 --max-complexity=10 src/my_package

Refactoring strategies

Extract helper functions:

# Before: Complex function with many branches
def process_order(order):
    if order.type == "retail":
        # 20 lines of retail logic
        ...
    elif order.type == "wholesale":
        # 20 lines of wholesale logic
        ...
    # more branches...

# After: Simplified with helpers
def process_order(order):
    handlers = {
        "retail": process_retail_order,
        "wholesale": process_wholesale_order,
    }
    handler = handlers.get(order.type, process_default_order)
    return handler(order)

Use early returns:

# Before: Nested conditionals
def validate(data):
    if data:
        if data.get("name"):
            if len(data["name"]) > 0:
                return True
    return False

# After: Early returns
def validate(data):
    if not data:
        return False
    if not data.get("name"):
        return False
    return len(data["name"]) > 0

Replace conditionals with polymorphism:

# Use classes or strategy pattern instead of long if/elif chains

Why WARNING severity?

This check is a WARNING because:

Complexity thresholds are subjective
Some complex functions are unavoidable
Context matters for complexity decisions

Configuration

Set complexity threshold

[tool.pycmdcheck]
max_complexity = 10

Skip this check

[tool.pycmdcheck]
skip = ["CQ005"]

CLI

pycmdcheck --skip CQ005