complexipy

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

Installation • Quick Start • Integrations • Documentation • Changelog • Complexipy Teams

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

# Show deterministic refactor suggestions for failing functions
complexipy . --failed --suggest-refactors

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

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

# Write 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

# Fail only on threshold-breaking regressions in a diff
complexipy . --diff main
# Analyze current directory while excluding files or directories with glob patterns
complexipy . --exclude "tests/**" --exclude "path/to/exclude.py"

# Disregard all inline ignore comments
complexipy . --no-ignore

# Report all ignored functions
complexipy . --report-ignored

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

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

- name: Run complexipy
  run: complexipy . --output-format sarif --output complexipy-results.sarif --ignore-complexity

- name: Upload SARIF results
  uses: github/codeql-action/upload-sarif@v3
  with:
      sarif_file: complexipy-results.sarif

complexity:
    image: python:3.11
    script:
        - pip install complexipy
        - complexipy . --output-format gitlab --output complexipy-code-quality.json --ignore-complexity
    artifacts:
        when: always
        reports:
            codequality: complexipy-code-quality.json

repos:
    - repo: https://github.com/rohaquinlop/complexipy-pre-commit
      rev: v5.1.0
      hooks:
          - id: complexipy

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 = []
check-script = false
no-ignore = false
report-ignored = false
output-format = ["json", "sarif"]
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
no-ignore = false
report-ignored = false
output-format = ["json"]
output = "complexipy-results.json"

Legacy TOML keys and CLI flags such as output-json = true and --output-json were removed. Use output-format and --output-format instead. See the migration note for the full list of removed flags and keys with their replacements.

Diff Configuration

The comparison policy can be declared once in the repo, so CI jobs and contributors don't repeat --diff flags:

# complexipy.toml or .complexipy.toml
[diff]
branch = "main"
staged = true

# pyproject.toml
[tool.complexipy.diff]
branch = "main"
staged = true

branch makes a plain complexipy . behave like complexipy . --diff main (enforcement included); staged enables staged comparison by default. CLI flags always take precedence. See the usage guide for details, including the empty-branch opt-out and missing-reference behavior.

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

CLI Options

Example:

# Exclude a directory recursively under the provided root
complexipy . --exclude "tests/**"
# Exclude a specific file
complexipy . --exclude "src/legacy/old_code.py"

Refactor Suggestions

Use --suggest-refactors to print a small, ranked set of deterministic refactor plans next to rich CLI results:

complexipy . --failed --suggest-refactors

Sample output (abbreviated -- the real output also shows a caret-underlined span, the surrounding source, and a documentation link):

      [1] C007 Merge nested if statements
          --> sample.py:4:9
          Category: • Readability | Applicability: * Safe to apply
          Lines 4-6 -> Estimated reduction: -2 complexity (6 -> 4)

          Suggestion: * Safe to apply
          Merge nested conditions into `if item.active and item.ready:`

Plans are based on the Rust AST analysis only; no AI is used and no code is rewritten automatically. Estimated reductions are approximate, ranked, and limited, so treat them as guidance rather than exact future scores. --plain --suggest-refactors keeps plain output unchanged.

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

By default --diff enforces the complexity threshold: the run exits with code 1 only when a change breaches the contract relative to --max-complexity-allowed:

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

Functions that regress but stay at or below the threshold (e.g. 3 → 4 with -mx 15) are not flagged — the threshold is still the main contract, and --diff only catches regressions that actually break it.

To see the diff visually without affecting the exit code, use --diff-only instead:

complexipy . --diff-only HEAD~1

To compare the staged (git index) content instead of the working tree — "what complexity am I about to commit?" — add --staged:

# Staged changes vs HEAD (the default baseline for --staged)
complexipy . --staged

# Staged changes vs a specific ref
complexipy . --diff main --staged

Like --diff, --staged enforces the threshold against the staged content and fails when a staged change pushes a function above --max-complexity-allowed. Staged deletions produce REMOVED entries and staged additions NEW entries.

Requires git to be available and the analysed paths to be inside a git repository.

Script Complexity

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

# Report top-level script logic as <module>
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, similar to Ruff's C901 ignores:

def legacy_adapter(x, y):  # complexipy: ignore
    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 or plain text, it's ignored by the parser.

Disabling Inline Ignores

Use --no-ignore to disregard all inline ignore comments and analyze every function:

# Treat every function equally, regardless of suppression
complexipy . --no-ignore

Functions previously suppressed by # complexipy: ignore or # noqa: complexipy will be analyzed normally and may fail the threshold.

Reporting Ignored Functions

Use --report-ignored to list every location where an ignore comment suppresses a function:

# List ignored functions
complexipy . --report-ignored

# Combine with --no-ignore to report while analyzing everything
complexipy . --report-ignored --no-ignore

When --output-format json is also active, ignored locations are exported to complexipy-ignored.json. The report prints even under --quiet.

Both flags are also available in the Python API via no_ignore=True on file_complexity() and code_complexity(). To programmatically collect ignored locations, use collect_all_ignored_locations() from the complexipy package.

API Reference

# Core functions
file_complexity(path: str, check_script: bool = False, no_ignore: bool = False) -> FileComplexity
code_complexity(source: str, check_script: bool = False, no_ignore: bool = False) -> CodeComplexity
collect_all_ignored_locations(paths: List[str], exclude: List[str] = [], invocation_path: str = "") -> Tuple[List[IgnoredLocation], List[str]]

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

FunctionComplexity:
  ├─ name: str
  ├─ complexity: int
  ├─ line_start: int
  ├─ line_end: int
  ├─ line_complexities: List[LineComplexity]
  └─ refactor_plans: List[RefactorPlan]

RefactorPlan:
  ├─ kind: str
  ├─ title: str
  ├─ line_start: int
  ├─ line_end: int
  ├─ column_start: int
  ├─ current_complexity: int
  ├─ estimated_reduction: int
  ├─ estimated_complexity_after: int
  ├─ rule_id: str
  ├─ category: RuleCategory
  ├─ applicability: Applicability
  ├─ description: str
  ├─ explanation: str
  ├─ references: List[str]
  ├─ suggestion: Optional[CodeSuggestion]
  ├─ help: Optional[str]
  └─ doc_url: str

CodeSuggestion:
  ├─ replacement: str
  ├─ applicability: Applicability
  └─ description: str

RuleCategory: Complexity | Readability
Applicability: MachineApplicable | MaybeIncorrect | Informational

LineComplexity:
  ├─ line: int
  └─ complexity: int

IgnoredLocation:
  ├─ path: str
  ├─ line: int
  └─ comment: str

CodeComplexity:
  ├─ complexity: int
  └─ functions: List[FunctionComplexity]