Rule catalog¶

pyscn ships 32 rules across 7 categories. Every rule has a page that describes what it detects, why it's a problem, a bad example, and how to fix it.

Click a rule name to open its page.

Unreachable Code¶

Dead code that can never execute. Detected through control-flow graph reachability analysis.

Rule	Severity
`unreachable-after-return`	Critical
`unreachable-after-raise`	Critical
`unreachable-after-break`	Critical
`unreachable-after-continue`	Critical
`unreachable-after-infinite-loop`	Warning
`unreachable-branch`	Warning

Duplicate Code¶

Copy-paste or near-copy-paste code fragments across the project.

Rule	Severity
`duplicate-code-identical`	Warning
`duplicate-code-renamed`	Warning
`duplicate-code-modified`	Info (opt-in)
`duplicate-code-semantic`	Warning

Complexity¶

Functions that are too branchy to test or reason about reliably.

Rule	Severity
`high-cyclomatic-complexity`	By threshold

Class Design¶

Classes that depend on too many things or do too many unrelated jobs.

Rule	Severity
`high-class-coupling`	By threshold
`low-class-cohesion`	By threshold

Dependency Injection¶

Constructor and collaborator patterns that hurt testability.

Rule	Severity
`too-many-constructor-parameters`	Warning
`global-state-dependency`	Error
`module-variable-dependency`	Warning
`singleton-pattern-dependency`	Warning
`concrete-type-hint-dependency`	Info
`concrete-instantiation-dependency`	Warning
`service-locator-pattern`	Warning

Module Structure¶

Import graph problems: cycles, long chains, layer violations.

Rule	Severity
`circular-import`	By cycle size
`deep-import-chain`	Info
`layer-violation`	By architecture rule
`low-package-cohesion`	Warning

Mock Data¶

Placeholder data accidentally shipped to production.

Rule	Severity
`mock-keyword-in-code`	Info / Warning
`mock-domain-in-string`	Warning
`mock-email-address`	Warning
`placeholder-phone-number`	Warning
`placeholder-uuid`	Warning
`placeholder-comment`	Info
`repetitive-string-literal`	Info
`test-credential-in-code`	Warning

Selecting rules on the command line¶

Most users run all rules with pyscn analyze. For CI, filter by analyzer category:

pyscn check --select deadcode          # only unreachable-code rules
pyscn check --select clones            # only duplicate-code rules
pyscn check --select complexity        # only high-cyclomatic-complexity
pyscn check --select deps              # circular-import + deep-import-chain + layer-violation
pyscn check --select di                # all dependency-injection rules (opt-in)
pyscn check --select mockdata          # all mock-data rules (opt-in)
pyscn check --select complexity,deadcode,deps   # combine

See pyscn check for the full flag list.

Severity meanings¶

Severity	Intent
Critical	Almost always a bug. Prefer fixing before merging.
Error	High-risk pattern. Usually should fail CI.
Warning	Worth reviewing. Default fail threshold for `pyscn check`.
Info	Informational. Surfaces only when `min_severity = "info"` or equivalent.
By threshold	Severity depends on a numeric threshold (see the rule's Options).