Python中Literal 类型的具体使用

from typing import Literal

def always_true() -> Literal[True]:
    return True

def open_read_only(file: str) -> str:
    # 返回值只能是特定的字符串字面量
    return "success"

def process_status(code: Literal[200, 404, 500]) -> str:
    if code == 200:
        return "OK"
    elif code == 404:
        return "Not Found"
    else:
        return "Server Error"

# 定义文件模式类型
FileMode = Literal['r', 'rb', 'w', 'wb', 'a', 'ab']

def open_file(filepath: str, mode: FileMode) -> str:
    # 实现文件打开逻辑
    return f"File {filepath} opened with mode {mode}"

# 正确的用法
open_file("data.txt", "r")      # 通过类型检查
open_file("data.bin", "rb")     # 通过类型检查

# 错误的用法（类型检查器会报错）
open_file("data.txt", "read")   # 错误：'read' 不是有效的字面量

# 布尔值字面量
def toggle_switch(state: Literal[True, False]) -> Literal[True, False]:
    return not state

# 数字字面量
Direction = Literal[0, 90, 180, 270]

def rotate_sprite(angle: Direction) -> None:
    print(f"Rotating to {angle} degrees")

# 混合类型字面量
ResponseType = Literal["success", "error", 200, 404]

from typing import Union, Literal

# 更灵活的类型定义
StatusCode = Union[Literal[200], Literal[404], Literal[500]]
ApiResponse = Union[dict, Literal["timeout"], Literal["error"]]

# 使用 Literal 代替简单的枚举
Color = Literal["red", "green", "blue", "yellow"]

def set_traffic_light(color: Color) -> None:
    if color == "red":
        print("Stop")
    elif color == "green":
        print("Go")
    elif color == "yellow":
        print("Caution")

# 类型检查会捕获拼写错误
set_traffic_light("red")    # 正确
set_traffic_light("reed")   # 类型检查错误

from typing import Literal, ClassVar

class DatabaseConnection:
    # 类常量使用 Literal 类型
    SUPPORTED_VERSIONS: ClassVar[Literal["1.0", "2.0", "3.0"]] = ["1.0", "2.0", "3.0"]
    
    def __init__(self, version: Literal["1.0", "2.0", "3.0"]):
        self.version = version
    
    @classmethod
    def get_status(cls) -> Literal["connected", "disconnected", "error"]:
        return "connected"

from typing import Literal, TypedDict

class ApiResponse(TypedDict):
    status: Literal["success", "error"]
    data: dict
    message: str

def handle_response(response: ApiResponse) -> None:
    if response["status"] == "success":
        process_data(response["data"])
    else:
        log_error(response["message"])

from typing import Literal, TypedDict

class AppConfig(TypedDict):
    environment: Literal["development", "staging", "production"]
    log_level: Literal["DEBUG", "INFO", "WARNING", "ERROR"]
    database: Literal["mysql", "postgresql", "sqlite"]

def validate_config(config: AppConfig) -> bool:
    # 配置验证逻辑
    return True

from typing import Literal

OrderState = Literal["pending", "confirmed", "shipped", "delivered", "cancelled"]

class Order:
    def __init__(self):
        self.state: OrderState = "pending"
    
    def transition(self, new_state: OrderState) -> None:
        # 状态转换逻辑
        valid_transitions = {
            "pending": ["confirmed", "cancelled"],
            "confirmed": ["shipped", "cancelled"],
            "shipped": ["delivered"],
        }
        
        if new_state in valid_transitions.get(self.state, []):
            self.state = new_state
        else:
            raise ValueError(f"Invalid transition from {self.state} to {new_state}")

from typing import Literal, Union

# 各种使用场景的完整示例
HttpMethod = Literal["GET", "POST", "PUT", "DELETE", "PATCH"]
StatusCode = Literal[200, 201, 400, 401, 403, 404, 500]
ApiResponse = Union[dict, list, Literal["error", "timeout", "unauthorized"]]

def make_api_request(
    method: HttpMethod,
    endpoint: str,
    expected_status: StatusCode = 200
) -> ApiResponse:
    """
    发起 API 请求
    
    Args:
        method: HTTP 方法，必须是预定义的字面量值
        endpoint: API 端点
        expected_status: 期望的 HTTP 状态码
    
    Returns:
        API 响应数据或错误字面量
    """
    # 实现请求逻辑
    if method == "GET":
        return {"data": "sample response"}
    else:
        return "error"