Python 3.14+ Expert Best Practices

Simple, pragmatic, opinionated. Only what matters for writing production-grade python code.

When to Apply

Reference these guidelines when:

• Writing Python functions, classes, or modules
• Reviewing Python code for error handling issues
• Refactoring existing Python codebases
• Implementing data validation and API boundaries
• Optimizing error detection and debugging patterns

Rule Categories by Priority

Priority	Category	Impact	Prefix
1	Error Handling	CRITICAL	dict-, operators-
2	Common Bugs	CRITICAL-HIGH	no-mutable-, no-generic-
3	Code Clarity	HIGH-MEDIUM	listcomp-, no-inline-
4	Code Style	LOW	avoid-, unnecessary-

Quick Reference

• dict-required-keys - Use d[key] for required dictionary keys to fail fast with KeyError
• no-mutable-defaults - No mutable defaults in function/method parameters
• operators-return-notimplemented - Return NotImplemented for unsupported operand types and design + vs += intentionally
• no-generic-except - Avoid generic except clauses to prevent hiding unexpected errors
• listcomp-no-side-effects - List comprehensions must produce a value you use (no side-effect listcomps)
• no-inline-imports - Place all import statements at the top of the file
• avoid-explanatory-comments - Avoid unnecessary comments for self-documenting code
• unnecessary-else-blocks - Avoid unnecessary else blocks after return/break/continue statements

How to Use

Read individual rule files for detailed explanations and code examples:

rules/dict-required-keys.md
rules/no-mutable-defaults.md
rules/operators-return-notimplemented.md
rules/no-generic-except.md
rules/listcomp-no-side-effects.md
rules/no-inline-imports.md
rules/avoid-explanatory-comments.md
rules/unnecessary-else-blocks.md

Each rule file contains:

• Brief explanation of why it matters
• When to use and when not to use the pattern
• Implementation requirements
• Incorrect code example with explanation
• Correct code example with explanation
• Additional context and references