python-style
Python coding style enforcement (PEP standards, type hints, docstrings, modern patterns). Auto-loads when writing or reviewing Python code.
What this skill does
# Python Style Best Practices Skill
This skill automatically activates when writing Python code to ensure consistency with PEP standards, type hints, and modern Python idioms.
## Core Standards
- **PEP 8**: Naming conventions, imports, line length
- **Type Hints**: Modern syntax (`list[str]` not `List[str]`, `X | None` not `Optional[X]`)
- **Docstrings**: Google style with Args, Returns, Raises sections
- **Imports**: stdlib → third-party → local, alphabetically sorted
## Naming Conventions
```python
# Classes: PascalCase
class UserAccount:
pass
# Functions/variables: snake_case
def calculate_total():
user_name = "john"
# Constants: SCREAMING_SNAKE_CASE
MAX_RETRY_COUNT = 3
# Private: single underscore prefix
def _internal_helper():
pass
```
## Type Hints (Python 3.10+)
```python
# Use built-in generics
def process(items: list[str]) -> dict[str, int]:
pass
# Use | for Optional/Union
def find_user(id: str) -> User | None:
pass
# TypedDict for structured dicts
class UserData(TypedDict):
id: str
name: str
```
## Function Length Guidelines
- **< 30 lines**: Ideal
- **30-50 lines**: Review for refactoring
- **> 50 lines**: Must be broken down
## Anti-Patterns to Avoid
- Missing type hints
- Bare `except:` clauses
- Magic numbers/strings without constants
- Non-expressive variable names (`d`, `temp`, `x`)
- Vague function names (`process`, `handle`, `do_stuff`)
## Merge-Friendly Patterns (for Parallel Development)
When multiple agents modify the same module, follow these patterns to enable automatic merge resolution by semantic merge tools (mergiraf).
### Always Run Ruff Before Commit
```bash
uv run ruff format .
uv run ruff check --fix .
```
This ensures imports are consistently ordered, enabling clean merges.
### `__all__` Must Be Alphabetical
Enable **RUF022** in ruff to enforce this automatically:
```toml
[tool.ruff.lint]
select = [
# ... other rules
"RUF022", # unsorted-dunder-all (enforces alphabetical __all__)
]
```
```python
# CORRECT - alphabetical, one per line, no comments
__all__ = [
"ACLFilterSpec",
"Chunk",
"ChunkerInterface",
"Document",
"QueryACLContext",
"Visibility",
]
# WRONG - grouped by category (causes merge conflicts)
__all__ = [
# Types
"Chunk",
"Document",
# Interfaces
"ChunkerInterface",
]
```
### No Comments Inside Lists
Comments inside `__all__`, import groups, or other lists break deterministic ordering and cause merge conflicts. Keep comments outside:
```python
# ACL and schema types exported for public API
__all__ = [
"ACLFilterSpec",
"Chunk",
"Document",
]
```
### When Adding to Shared Files (`__init__.py`, etc.)
1. Add new exports in **alphabetical position**
2. Never reorder existing exports
3. Run `ruff format` immediately after changes
4. Avoid adding section comments
### Why This Matters
Semantic merge tools like mergiraf can automatically resolve conflicts when:
- Both branches add items to the same list in alphabetical order
- No comments or groupings change the structure
- Formatting is consistent (via ruff)
Without these patterns, parallel agents adding exports to the same `__init__.py` will create conflicts requiring manual resolution.
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