Typing 模块使用指南

# 变量类型注解
name: str = "Alice"
age: int = 30
height: float = 1.75
is_student: bool = True

# 函数参数和返回值的类型注解
def greet(name: str) -> str:
    return f"Hello, {name}"

def calculate_area(length: float, width: float) -> float:
    return length * width

from typing import List, Dict, Tuple, Set

# 列表
numbers: List[int] = [1, 2, 3, 4, 5]

# 字典
person: Dict[str, str] = {"name": "Alice", "city": "New York"}

# 元组
coordinates: Tuple[float, float] = (40.7128, -74.0060)

# 集合
unique_numbers: Set[int] = {1, 2, 3, 4, 5}

from typing import Union, Optional, Any, Callable

# Union: 多个可能类型
def process_input(value: Union[str, int]) -> None:
    pass

# Optional: 可能是None
def find_user(user_id: int) -> Optional[str]:
    # 返回用户名或None
    pass

# Any: 任意类型
def process_data(data: Any) -> Any:
    pass

# Callable: 函数类型
def apply_function(func: Callable[[int, int], int], x: int, y: int) -> int:
    return func(x, y)

from typing import TypeVar, NewType

# 类型别名
UserId = int
users: Dict[UserId, str] = {1: "Alice", 2: "Bob"}

# 新类型
UserId = NewType('UserId', int)
user_id = UserId(12345)

# 泛型类型变量
T = TypeVar('T')
def first_item(items: List[T]) -> T:
    return items[0]

from typing import Literal, Final

# Literal: 特定值
def set_direction(direction: Literal["north", "south", "east", "west"]) -> None:
    pass

# Final: 不可重新赋值
MAX_SIZE: Final[int] = 100

from typing import ClassVar

class Person:
    # 类变量类型注解
    species: ClassVar[str] = "Homo sapiens"
    
    def __init__(self, name: str, age: int) -> None:
        self.name = name
        self.age = age
    
    def get_birth_year(self) -> int:
        return 2023 - self.age

from typing import List, Dict, Optional

def process_users(users: List[Dict[str, str]]) -> List[str]:
    """处理用户列表，返回用户名列表"""
    return [user["name"] for user in users if "name" in user]

def calculate_stats(data: List[float]) -> Dict[str, float]:
    """计算数据的统计信息"""
    return {
        "mean": sum(data) / len(data),
        "max": max(data),
        "min": min(data)
    }

# 使用类型提示的完整示例
class Database:
    def __init__(self, connection_string: str) -> None:
        self.connection_string = connection_string
    
    def query(self, query: str) -> Optional[List[Dict]]:
        # 模拟数据库查询
        return [{"id": 1, "name": "Alice"}, {"id": 2, "name": "Bob"}]

def get_user_names(db: Database) -> List[str]:
    results = db.query("SELECT name FROM users")
    if results is None:
        return []
    return [user["name"] for user in results]