Cyclomatic Complexity

A function's cyclomatic complexity = number of independent paths through it. Roughly:

complexity = 1 + (count of branches: if, elif, while, for, except, and, or, ternary, case)

Why measure?

• Higher complexity → harder to test (more paths to cover).
• Empirically, complexity > 10 correlates with bugs.

Common thresholds:

• ≤ 10: green.
• 11-20: yellow (review).

• 20: red (refactor).

Other complexity metrics:

• Cognitive complexity: similar but penalizes nesting more.
• Halstead metrics: ops + operands.
• NPath: counts unique acyclic paths (can explode).

Linter typically reports cyclomatic; humans read the function.