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-format json --output-format csv

# Show the top 5 most complex functions
complexipy . --top 5

# Emit plain text for scripting/AI agents
complexipy . --plain

# Include module-level script complexity as <module>
complexipy . --check-script

# Save a GitLab report to a deterministic path
complexipy . --output-format gitlab --output complexipy-code-quality.json

# Compare complexity against a git reference
complexipy . --diff HEAD~1
# 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", check_script=True)
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, check_script=True)
print(f"Complexity: {result.complexity}")

Integrations¶

🔧 GitHub Actions

- uses: rohaquinlop/complexipy-action@v2
  with:
      paths: .
      max_complexity_allowed: 10
      output_format: json

🪝 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](https://marketplace.visualstudio.com/items?itemName=rohaquinlop.complexipy) 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:

complexipy.toml (project-specific config)
.complexipy.toml (hidden config file)
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 = []
check-script = false
output-format = ["json", "gitlab"]
output = "reports/"

# 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 = []
check-script = false
output-format = ["json"]
output = "complexipy-results.json"

Legacy TOML keys such as output-json = true and CLI flags such as --output-json still work for now, but they are deprecated in favor of output-format and --output-format.

check-script is supported in TOML. --top and --plain are CLI-only flags.

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\\|file_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	-
`--top <n>`	Show only the `n` most complex functions, globally sorted by complexity descending	—
`--plain`	Emit plain text lines as `<path> <function> <complexity>`. Cannot be combined with `--quiet`	`false`
`--output-format <format>`	Select a machine-readable output format. Repeat the flag for multiple formats (`json`, `csv`, `gitlab`, `sarif`)	—
`--output <path>`	Write machine-readable output to a file or directory. Use a directory when emitting multiple formats	—
`--diff <ref>`	Show a complexity diff against a git reference (e.g. `HEAD~1`, `main`)	—
`--ratchet`, `-R`	With `--diff`, fail only when a change pushes a function above `--max-complexity-allowed` (or makes an already-over function worse). See Ratchet Mode	`false`
`--check-script`	Report module-level (script) complexity as a synthetic `<module>` entry	`false`
`--output-json`	Deprecated alias for `--output-format json`	`false`
`--output-csv`	Deprecated alias for `--output-format csv`	`false`
`--output-gitlab`	Deprecated alias for `--output-format gitlab`	`false`
`--output-sarif`	Deprecated alias for `--output-format sarif`	`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).

Complexity Diff¶

Compare complexity against any git reference to see whether a branch or commit made things better or worse:

# Compare the working tree against the previous commit
complexipy . --diff HEAD~1

# Compare against a named branch
complexipy . --diff main

The diff is appended after the normal analysis output and does not affect the exit code. Requires git to be available and the analysed paths to be inside a git repository.

Ratchet Mode¶

Add --ratchet (-R) on top of --diff to turn it into a regression-only gate for CI:

complexipy . --diff main --ratchet
complexipy . --diff HEAD~1 -R -mx 15

The run exits with code 1 only when:

a new function is introduced above --max-complexity-allowed, or
an existing function's complexity increases and ends above the threshold (already-over functions getting worse also fail).

Small upward changes that stay at or below the threshold (e.g. 3 → 4 with -mx 15) are not flagged — the threshold is still the main contract, and ratchet only catches regressions that actually break it. This makes it ideal for legacy codebases where you want to block regressions without fixing every existing offender first. See the Ratchet Mode section for more detail.

Script Complexity¶

Use --check-script when you also want to score module-level control flow, not just functions:

complexipy scripts/bootstrap.py --check-script

The same capability is available in the Python API via check_script=True on both file_complexity() and code_complexity().

Inline Ignores¶

You can explicitly ignore a known complex function inline using # complexipy: ignore:

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

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

Note: The # noqa: complexipy syntax is deprecated. Tools like yesqa strip unrecognized # noqa comments, which would silently remove your suppressions. Migrate to # complexipy: ignore to avoid this issue.

API Reference¶

# Core functions
file_complexity(path: str, check_script: bool = False) -> FileComplexity
code_complexity(source: str, check_script: bool = False) -> 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](https://rohaquinlop.github.io/complexipy/) • [PyPI](https://pypi.org/project/complexipy/) • [GitHub](https://github.com/rohaquinlop/complexipy)** _{Built with ❤️ by @rohaquinlop and contributors}