python-best-practiceslisted
Install: claude install-skill aiskillstore/marketplace
# Python Best Practices
Follows type-first, functional, and error handling patterns from CLAUDE.md. This skill covers language-specific idioms only.
## Make Illegal States Unrepresentable
Use Python's type system to prevent invalid states at type-check time.
**Frozen dataclasses for immutable domain models:**
```python
from dataclasses import dataclass
from datetime import datetime
@dataclass(frozen=True)
class User:
id: str
email: str
name: str
created_at: datetime
# Frozen dataclasses are immutable — no accidental mutation
```
**Discriminated unions with Literal:**
```python
from dataclasses import dataclass
from typing import Literal
@dataclass
class Success:
status: Literal["success"] = "success"
data: str
@dataclass
class Failure:
status: Literal["error"] = "error"
error: Exception
RequestState = Success | Failure
def handle_state(state: RequestState) -> None:
match state:
case Success(data=data):
render(data)
case Failure(error=err):
show_error(err)
```
**NewType for domain primitives:**
```python
from typing import NewType
UserId = NewType("UserId", str)
OrderId = NewType("OrderId", str)
def get_user(user_id: UserId) -> User:
# Type checker prevents passing OrderId here
...
```
**Protocol for structural typing:**
```python
from typing import Protocol
class Readable(Protocol):
def read(self, n: int = -1) -> bytes: ...
def process_input(source: Readable) -> bytes: