modern-python-patterns

Modern Python Patterns

Modern Python patterns for 3.10+ emphasizing readability, type safety, and idiomaticity.

Core Principles

1. Type hints everywhere - Function signatures, class attributes, variables when unclear
2. Dataclasses over dicts - Structured data with validation
3. Pathlib over os.path - Object-oriented file paths
4. f-strings over .format() - Readable string formatting

Type Hints

Always annotate function signatures

from typing import Optional, Union
from collections.abc import Sequence

def process_items(
    items: Sequence[str],
    threshold: float = 0.5,
    max_count: Optional[int] = None
) -> list[str]:
    """Process items with optional limit."""
    return [item for item in items if len(item) > threshold]

Modern patterns (3.10+):

• Use list[str] not List[str] (PEP 585)
• Use str | None not Optional[str] (PEP 604)
• Use collections.abc not typing for abstract types

See type-hints-examples.md for:

• Generic types with TypeVar
• Protocol classes for structural typing
• Literal types and type narrowing
• typing.cast() and type guards

Dataclasses

Use dataclasses for structured data

from dataclasses import dataclass, field

@dataclass
class Config:
    host: str
    port: int = 8080
    debug: bool = False
    tags: list[str] = field(default_factory=list)

Benefits:

• Auto-generated __init__, __repr__, __eq__
• Type validation with type hints
• Immutable with frozen=True
• Post-init processing with __post_init__

See dataclass-examples.md for:

• Validation patterns
• Inheritance and composition
• Integration with Pydantic
• Slots for memory optimization

Pattern Matching (3.10+)

Use match/case for complex conditionals

def process_response(response: dict) -> str:
    match response:
        case {"status": "success", "data": data}:
            return f"Success: {data}"
        case {"status": "error", "code": code, "message": msg}:
            return f"Error {code}: {msg}"
        case {"status": status}:
            return f"Unknown status: {status}"
        case _:
            return "Invalid response"