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).