Detector: Complexity

Detector: Complexity

Flags Python functions that exceed cyclomatic complexity or line-count thresholds.

Property	Value
Name	complexity
Tier	HEURISTIC
Languages	Python
External tool	None (uses Python ast)
LLM required	No
Confidence	0.95 (source), 0.60 (test files)

What it detects

Python functions with:

• Cyclomatic complexity > 10 (decision points: if, elif, for, while, except, and, or, assert, ternary)
• Body longer than 50 lines

How it works

1. Parses Python files with the ast module
2. Walks all FunctionDef and AsyncFunctionDef nodes
3. Calculates McCabe cyclomatic complexity and body line count
4. Flags functions exceeding either threshold

Severity

Condition	Severity
CC > 20 or lines > 150	HIGH
CC > 15 or lines > 100	MEDIUM
Above threshold	LOW

Test files (test_*.py, files under tests/) are always demoted to LOW severity with 0.60 confidence — complex tests are common and rarely worth refactoring.

Example finding

[COMPLEXITY] src/httpx/_multipart.py:DataField.render_headers
  Complex function: render_headers (cyclomatic complexity 14, 62 lines)
  Severity: MEDIUM, Confidence: 0.95

Observed accuracy

Repo	Findings	Notes
pip-tools	20	~100% TP, some in tests
httpx	31	~95% TP, ~15 in test files

Known limitations

• Python-only (no JS/TS, Go, or Rust complexity analysis)
• Thresholds are not yet configurable via sentinel.toml
• Test files produce accurate but low-value findings (severity demoted to mitigate)