python-code-review

name	python-code-review
description	Reviews Python code for type safety, async patterns, error handling, and common mistakes. Use when reviewing .py files, checking type hints, async/await usage, or exception handling.

Python Code Review

Quick Reference

Issue Type	Reference
Indentation, line length, whitespace, naming	references/pep8-style.md
Missing/wrong type hints, Any usage	references/type-safety.md
Blocking calls in async, missing await	references/async-patterns.md
Bare except, missing context, logging	references/error-handling.md
Mutable defaults, print statements	references/common-mistakes.md

Review Checklist

PEP8 Style

• 4-space indentation (no tabs)
• Line length ≤79 characters (≤72 for docstrings/comments)
• Two blank lines around top-level definitions, one within classes
• Imports grouped: stdlib → third-party → local (blank line between groups)
• No whitespace inside brackets or before colons/commas
• Naming: snake_case for functions/variables, CamelCase for classes, UPPER_CASE for constants
• Inline comments separated by at least two spaces

Type Safety

• Type hints on all function parameters and return types
• No Any unless necessary (with comment explaining why)
• Proper T | None syntax (Python 3.10+)

Async Patterns

• No blocking calls (time.sleep, requests) in async functions
• Proper await on all coroutines

Error Handling

• No bare except: clauses
• Specific exception types with context
• raise ... from to preserve stack traces

Common Mistakes

• No mutable default arguments
• Using logger not print() for output
• f-strings preferred over .format() or %
• Equality against a numeric constant also admits True/False and floats (True == 1, 1.0 == 1) — fail-closed checks must pin the type too (type(x) is int; isinstance admits bool as a subclass of int)

Valid Patterns (Do NOT Flag)

These patterns are intentional and correct - do not report as issues:

• Type annotation vs type assertion - Annotations declare types but are not runtime assertions; don't confuse with missing validation
• Using Any when interacting with untyped libraries - Required when external libraries lack type stubs
• Empty __init__.py files - Valid for package structure, no code required
• noqa comments - Valid when linter rule doesn't apply to specific case
• Using cast() after runtime type check - Correct pattern to inform type checker of narrowed type

Context-Sensitive Rules

Only flag these issues when the specific conditions apply:

Issue	Flag ONLY IF
Generic exception handling	Specific exception types are available and meaningful
Unused variables	Variable lacks _ prefix AND isn't used in f-strings, logging, or debugging

Gates (reporting workflow)

Complete in order. Do not advance until each pass condition is met.

1. Scope — Pass: You list every .py path (or explicit glob) you inspected this run.
2. False-positive screen — Pass: For each issue you plan to report, you checked Valid Patterns and Context-Sensitive Rules above; you drop or narrow the finding if those sections say not to flag it.
3. Evidence — Pass: Each remaining finding includes [FILE:LINE] (or a bounded line range). Symbols or short verbatim snippets may supplement the location anchor but do not replace it.
4. Verification protocol — Pass: You load review-verification-protocol and complete its mandatory steps for each reported issue before the user-facing write-up.
5. Ship — Pass: The user-visible output matches whatever structure that protocol requires (no issues-only dump that skips its checks).

When to Load References

• Reviewing code formatting/style → pep8-style.md
• Reviewing function signatures → type-safety.md
• Reviewing async def functions → async-patterns.md
• Reviewing try/except blocks → error-handling.md
• General Python review → common-mistakes.md

Review Questions

1. Does the code follow PEP8 formatting (indentation, line length, whitespace)?
2. Are imports properly grouped (stdlib → third-party → local)?
3. Do names follow conventions (snake_case, CamelCase, UPPER_CASE)?
4. Are all function signatures fully typed?
5. Are async functions truly non-blocking?
6. Do exceptions include meaningful context?
7. Are there any mutable default arguments?

Before reporting: complete Gates (reporting workflow) above (especially gate 4).