sqa-qc-checklists/qc-programming-python.md

Quality Criteria: Python Source Code

Metadata

Key	Value
ID	QC-PY-001
CrossReference	QC-DCD-001, QC-ADR-001
DomainLanguages	IT Professional English

Version History

Date	Status	Author	Reviewer	Change	Commit
2026-10-09	Deprecated	Jens Tirsvad Nielsen	S02	Added criteria 14 to 16 (DRY, dependency rule and SOLID)	304ec77
2026-10-09	Accepted	Jens Tirsvad Nielsen	S02	Accepted by the author as stand-in for S02 (Coding Standards Governance), through the pull request that merges this row; the delta re-review of the new criteria is a draft confirmed by the author as stand-in, not independently	b5e5613

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Purpose

Python source code is the implementation of the design. This checklist confirms that code follows the Python coding conventions (PEP 8 naming and layout, type hints, error handling), so that it is readable, maintainable and consistent with the design it implements.

Quality Criteria Checklist

Level: Mandatory criteria are the baseline every instance must meet; Optional criteria are advanced and may be deferred.

#	Criterion	Level	ISO/IEC 25010 Characteristic(s)	Notes
1	Packages, modules, functions, variables, classes and constants follow PEP 8 casing (snake_case, PascalCase, UPPER_SNAKE)	Mandatory	Maintainability, Usability
2	Names state purpose in the domain's language; no unexplained abbreviations, no single-letter names outside tiny scopes	Mandatory	Maintainability, Usability
3	Code is produced by the project's formatter and passes its linter with no unexplained suppressions	Mandatory	Maintainability
4	Every function and method signature is type-annotated, including -> None	Mandatory	Maintainability, Reliability
5	No bare except:, no swallowed exceptions; specific exceptions are raised and the cause is kept (raise ... from)	Mandatory	Reliability
6	No mutable default arguments and no shadowed builtins	Mandatory	Reliability, Maintainability
7	Files, locks and connections are managed with context managers	Mandatory	Reliability, Performance Efficiency
8	Public modules, classes and functions have docstrings that say what, not how	Optional	Usability, Maintainability
9	Logging uses logging, not print; no secrets or personal data in log output	Mandatory	Security, Maintainability
10	Classes and operations trace to the Design Class Diagram they implement; deviations are recorded	Mandatory	Functional Suitability, Maintainability
11	Tests exist for new behaviour, are named for the behaviour, and do not depend on order or the network	Mandatory	Reliability, Maintainability
12	Type checker runs in strict mode without errors; Any is justified in a comment	Optional	Reliability, Maintainability
13	Dependencies are declared and pinned in the project's dependency file, none unused	Optional	Portability, Security
14	Each piece of knowledge (a business rule, constant, format, validation or query) is defined in one place; code is merged only where it expresses the same knowledge, not where it merely looks alike	Mandatory	Maintainability	Modularity, Reusability. Rule: coding-conventions skill, “State each piece of knowledge once”
15	Imports point inward: business-rule modules import no framework, database, UI or delivery-mechanism code, and there are no import cycles	Mandatory	Maintainability, Portability	Modularity, Portability. Rule: coding-conventions skill, “Dependencies point inward”
16	SOLID holds: a class or module has one reason to change; new behaviour is added by extension, not by editing a type test in several places; subclasses honour the contract of their base; protocols are narrow; high-level code depends on protocols or abstract types and receives its implementations	Mandatory	Maintainability	Single responsibility is the most commonly violated. Rule: coding-conventions skill, “SOLID”

Common Defects

• Java- or C#-style casing (getTotal, customerList for functions and variables)
• Missing or partial type annotations
• Bare except: or except Exception: pass
• Mutable default arguments (def f(x=[]))
• print used for diagnostics; wildcard imports
• Code reformatted by hand, or an unrelated reformat mixed into a functional change
• Classes or methods that appear in no design artifact and have no stated reason
• The same rule, constant or validation written in two modules, or two functions merged because they look alike although they change for different reasons
• Business-rule modules importing the ORM, the web framework or a database driver
• A class with several unrelated responsibilities, or an isinstance chain repeated in several places

Traceability Rule

• Backward: Design Class Diagram checklist (QC-DCD-001) for the classes and operations being implemented; Architecture Decision Record checklist (QC-ADR-001) for the decisions that constrain the implementation
• Forward: none — source code is the end of the QC checklist chain

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