Python Typing Skill
Expert guidance for Python type hints and static type checking.
Modern Type Syntax
Future Annotations (Python 3.7+)
python
from __future__ import annotations
def process(items: list[str]) -> dict[str, int]:
"""Modern syntax without importing List, Dict."""
return {item: len(item) for item in items}
Union Types (Python 3.10+)
python
# Modern
def func(value: str | None = None) -> int | float:
pass
# Old style
from typing import Optional, Union
def func(value: Optional[str] = None) -> Union[int, float]:
pass
Type Hints Best Practices
Function Signatures
python
def greet(name: str, age: int) -> str:
return f"Hello {name}, age {age}"
Collections
python
from collections.abc import Sequence, Mapping
def process_items(items: Sequence[str]) -> Mapping[str, int]:
"""Accept any sequence, return any mapping."""
return {item: len(item) for item in items}
Callable Types
python
from collections.abc import Callable
def apply(func: Callable[[int], str], value: int) -> str:
return func(value)
Protocols (Structural Typing)
python
from typing import Protocol
class Drawable(Protocol):
def draw(self) -> None: ...
def render(obj: Drawable) -> None:
"""Accepts any object with draw() method."""
obj.draw()
Generics
python
from typing import TypeVar, Generic
T = TypeVar('T')
class Stack(Generic[T]):
def __init__(self) -> None:
self._items: list[T] = []
def push(self, item: T) -> None:
self._items.append(item)
def pop(self) -> T:
return self._items.pop()
Mypy Configuration
ini
# pyproject.toml [tool.mypy] python_version = "3.11" strict = true warn_return_any = true warn_unused_configs = true disallow_untyped_defs = true
Review Severity
- •MAJOR: Missing type hints on public APIs, using Any without justification
- •MINOR: Missing return type hints, using old Union syntax
- •SUGGESTION: Could use Protocol for duck typing, could use TypedDict