浅析python如何使用Literal限制函数参数的取值范围

from typing import Literal

from typing_extensions import Literal

from typing import Literal

def print_task_status(status: Literal["success", "failure", "pending"]) -> None:
    """打印任务状态，仅接受指定的3个值"""
    print(f"Task status: {status}")

print_task_status(“success”)
print_task_status(“pending”)

print_task_status("error")  # mypy 提示：Argument 1 to "print_task_status" has incompatible type "Literal['error']"; expected "Literal['success', 'failure', 'pending']"

from typing import Literal

def set_log_level(level: Literal[1, 2, 3]) -> None:
    """设置日志级别：1=DEBUG，2=INFO，3=ERROR"""
    level_map = {1: "DEBUG", 2: "INFO", 3: "ERROR"}
    print(f"Log level set to: {level_map[level]}")

set_log_level(2)

set_log_level(4) # 超出 1/2/3 范围

from typing import Literal

def get_config(key: Literal["timeout", "retry", 5]) -> str:
    """获取配置，key 仅支持指定字符串/数值"""
    config = {"timeout": "10s", "retry": "3次", 5: "特殊配置"}
    return config[key]

get_config(“timeout”)
get_config(5)

get_config(6) # mypy 报错

from typing import Literal, TypeAlias

#定义类型别名：限制仅支持这4种HTTP方法
HTTPMethod: TypeAlias = Literal["GET", "POST", "PUT", "DELETE"]

def send_request(url: str, method: HTTPMethod) -> None:
    """发送HTTP请求，method 仅支持指定方法"""
    print(f"Send {method} request to {url}")

send_request(“https://example.com”, “GET”)

send_request(“https://example.com”, “PATCH”) # mypy 报错

from typing import Literal

def print_status(status: Literal["success", "failure", "pending"]) -> None:
    # 运行时校验（兜底）
    valid_status = {"success", "failure", "pending"}
    if status not in valid_status:
        raise ValueError(f"Invalid status: {status}. Must be one of {valid_status}")
    print(status)
#运行时触发报错
print_status("error")  # ValueError: Invalid status: error. Must be one of {'success', 'failure', 'pending'}

#Python 3.7-
from typing_extensions import Literal

mypy test.py