Python 类型提示：类型系统的艺术

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

# 变量类型
age: int = 25
price: float = 19.99
is_active: bool = True

from typing import List, Dict, Set, Tuple

# 列表
names: List[str] = ["Alice", "Bob"]

# 字典
user: Dict[str, int] = {"age": 25, "score": 100}

# 集合
tags: Set[str] = {"python", "ai"}

# 元组（固定长度）
point: Tuple[int, int] = (10, 20)
person: Tuple[str, int, float] = ("Alice", 25, 1.65)

from typing import Optional

# Optional[X] 等价于 X | None
name: Optional[str] = None  # 可以是字符串或 None

# Python 3.10+ 可用
name: str | None = None

from typing import Union

# Union 可以是多种类型之一
result: Union[int, str] = 42  # int 或 str

# Python 3.10+ 可用
result: int | str = 42

from typing import TypeVar, Generic

T = TypeVar('T')

class Container(Generic[T]):
    def __init__(self, value: T):
        self.value = value
    
    def get(self) -> T:
        return self.value

# 使用
int_container = Container[int](42)
str_container = Container[str]("hello")

from typing import TypeVar

T = TypeVar('T')

def first(items: List[T]) -> T:
    """返回列表第一个元素"""
    return items[0]

# 类型自动推断
first([1, 2, 3])        # int
first(["a", "b", "c"])  # str
first([1, "a", 2.0])    # Union[int, str, float]

from typing import Protocol

class Drawable(Protocol):
    def draw(self) -> None: ...

class Circle:
    def draw(self) -> None:
        print("画圆")

class Square:
    def draw(self) -> None:
        print("画正方形")

# 只要有 draw 方法就能传入
def render(shape: Drawable) -> None:
    shape.draw()

render(Circle())   # OK
render(Square())  # OK

from typing import TypeVar

# 约束类型范围
Number = TypeVar('Number', int, float)

def add(a: Number, b: Number) -> Number:
    return a + b

add(1, 2)      # OK (int)
add(1.0, 2.0)  # OK (float)
add(1, 2.0)    # Error! 类型不一致

from typing import Callable, Any

# 函数作为参数
def apply(func: Callable[[int], int], value: int) -> int:
    return func(value)

def double(x: int) -> int:
    return x * 2

apply(double, 5)  # 10

# 可变参数
def call_twice(func: Callable[..., Any], *args, **kwargs):
    func(*args, **kwargs)
    func(*args, **kwargs)

from typing import Literal

# 限制为特定值
def set_status(status: Literal["pending", "success", "error"]) -> None:
    print(f"状态: {status}")

set_status("pending")  # OK
set_status("unknown")  # Error!

# 结合 Union
def process(mode: Literal["read"] | Literal["write"]) -> None:
    pass

from typing import List, Dict, Tuple

# 简单别名
UserId = int
Email = str

# 复杂类型别名
Response = Dict[str, str | int | bool]
Coordinate = Tuple[float, float]
Matrix = List[List[float]]

from typing import get_type_hints, get_origin, get_args

def greet(name: str) -> str:
    return f"Hello, {name}!"

# 获取类型提示
hints = get_type_hints(greet)
# {'name': <class 'str'>, 'return': <class 'str'>}

# 检查泛型
List[str]           # get_origin() -> list
List[str]           # get_args() -> (str,)

from pydantic import BaseModel

class User(BaseModel):
    name: str
    age: int
    email: str | None = None

# 自动类型验证
user = User(name="Alice", age=25)
# 错误类型会自动转换或报错

# 安装 mypy
pip install mypy

# 运行检查
mypy your_module.py

# 配置 pyproject.toml
# [tool.mypy]
# python_version = "3.11"
# warn_return_any = true
# warn_unused_configs = true