complexipy 5.2.0

An extremely fast Python library to calculate the cognitive complexity of Python files, written in Rust.

complexipy

Blazingly fast cognitive complexity analysis for Python, written in Rust.

Installation • Quick Start • Integrations • Documentation

What is Cognitive Complexity?

Cognitive complexity measures how hard code is to understand by humans, not machines.

Unlike traditional metrics like cyclomatic complexity, cognitive complexity accounts for nesting depth and control flow patterns that affect human comprehension. Inspired by G. Ann Campbell's research at SonarSource, complexipy provides a fast, accurate implementation for Python.

Key benefits:

• Human-focused - Penalizes nesting, flow breaks, and human-unfriendly logic
• Actionable insights - Identifies genuinely hard-to-maintain code
• Different from cyclomatic - Measures readability while cyclomatic measures structural, testing, and branch density

Common Questions

How is complexity calculated? Learn about the scoring algorithm, what each control structure contributes, and how nesting affects the final score.

How does this compare to Ruff's PLR0912? Understand the key differences between cyclomatic complexity (Ruff) and cognitive complexity (complexipy), and why you might want to use both.

Is this a SonarSource/Sonar product? No. complexipy is an independent project inspired by G. Ann Campbell's research, but it's not affiliated with or endorsed by SonarSource.

Installation

pip install complexipy
# or
uv add complexipy

Quick Start

Command Line

# Analyze current directory
complexipy .

# Analyze specific file/directory
complexipy path/to/code.py

# Analyze with custom threshold
complexipy . --max-complexity-allowed 10

# Save results to JSON/CSV
complexipy . --output-json --output-csv

# Analyze current directory while excluding specific files
complexipy . --exclude path/to/exclude.py --exclude path/to/other/exclude.py

Python API

from complexipy import file_complexity, code_complexity

# Analyze a file
result = file_complexity("app.py")
print(f"File complexity: {result.complexity}")

for func in result.functions:
    print(f"{func.name}: {func.complexity}")

# Analyze code string
snippet = """
def complex_function(data):
    if data:
        for item in data:
            if item.is_valid():
                process(item)
"""

result = code_complexity(snippet)
print(f"Complexity: {result.complexity}")

Integrations

🔧 GitHub Actions

- uses: rohaquinlop/complexipy-action@v2
  with:
    paths: .
    max_complexity_allowed: 10
    output_json: true

🪝 Pre-commit Hook

repos:
- repo: https://github.com/rohaquinlop/complexipy-pre-commit
  rev: v4.2.0
  hooks:
    - id: complexipy

🔌 VS Code Extension

Install from the marketplace for real-time complexity analysis with visual indicators.

Configuration

TOML Configuration Files

complexipy supports configuration via TOML files. Configuration files are loaded in this order of precedence:

1. complexipy.toml (project-specific config)
2. .complexipy.toml (hidden config file)
3. pyproject.toml (under [tool.complexipy] section)

Example Configuration

# complexipy.toml or .complexipy.toml
paths = ["src", "tests"]
max-complexity-allowed = 10
snapshot-create = false
snapshot-ignore = false
quiet = false
ignore-complexity = false
failed = false
color = "auto"
sort = "asc"
exclude = []
output-csv = false
output-json = false

# pyproject.toml
[tool.complexipy]
paths = ["src", "tests"]
max-complexity-allowed = 10
snapshot-create = false
snapshot-ignore = false
quiet = false
ignore-complexity = false
failed = false
color = "auto"
sort = "asc"
exclude = []
output-csv = false
output-json = false

CLI Options

Flag	Description	Default
--exclude	Exclude entries relative to each provided path. Entries resolve to existing directories (prefix match) or files (exact match). Non-existent entries are ignored.
--max-complexity-allowed	Complexity threshold	15
--snapshot-create	Save the current violations above the threshold into complexipy-snapshot.json	false
--snapshot-ignore	Skip comparing against the snapshot even if it exists	false
--failed	Show only functions above the complexity threshold	false
--color <auto|yes|no>	Use color	auto
--sort <asc|desc|name>	Sort results	asc
--quiet	Suppress output	false
--ignore-complexity	Don't exit with error on threshold breach	false
--version	Show installed complexipy version and exit	-
--output-json	Save results as JSON	false
--output-csv	Save results as CSV	false

Example:

# Exclude only top-level 'tests' directory under the provided root
complexipy . --exclude tests
# This will not exclude './complexipy/utils.py' if you pass '--exclude utils' at repo root,
# because there is no './utils' directory or file at that level.

Snapshot Baselines

Use snapshots to adopt complexipy in large, existing codebases without touching every legacy function at once.

# Record the current state (creates complexipy-snapshot.json in the working directory)
complexipy . --snapshot-create --max-complexity-allowed 15

# Block regressions while allowing previously-recorded functions
complexipy . --max-complexity-allowed 15

# Temporarily skip the snapshot gate
complexipy . --snapshot-ignore

The snapshot file only stores functions whose complexity exceeds the configured threshold. When a snapshot file exists, complexipy will automatically:

• fail if a new function crosses the threshold,
• fail if a tracked function becomes more complex, and
• pass (and update the snapshot) when everything is stable or improved, automatically removing entries that now meet the standard.

Use --snapshot-ignore if you need to temporarily bypass the snapshot gate (for example during a refactor or while regenerating the baseline).

Inline Ignores

You can explicitly ignore a known complex function inline, similar to Ruff's C901 ignores:

def legacy_adapter(x, y):  # noqa: complexipy (safe wrapper)
    if x and y:
        return x + y
    return 0

Place # noqa: complexipy on the function definition line (or the line immediately above). An optional reason can be provided in parentheses or plain text, it’s ignored by the parser.

API Reference

# Core functions
file_complexity(path: str) -> FileComplexity
code_complexity(source: str) -> CodeComplexity

# Return types
FileComplexity:
  ├─ path: str
  ├─ complexity: int
  └─ functions: List[FunctionComplexity]

FunctionComplexity:
  ├─ name: str
  ├─ complexity: int
  ├─ line_start: int
  └─ line_end: int

---

_{Inspired by the Cognitive Complexity research by G. Ann Campbell
complexipy is an independent project and is not affiliated with or endorsed by SonarSource}

Documentation • PyPI • GitHub

_{Built with ❤️ by @rohaquinlop and contributors}