Python Optional类型详解 - 可选值与空值处理指南

from typing import Optional

# 基本用法
def func(param: Optional[str]) -> None:
    ...

# 等价于
def func(param: Union[str, None]) -> None:
    ...

# 带默认值
def func(param: Optional[str] = None) -> None:
    ...

# 返回值可能为空
def find_user(user_id: int) -> Optional[dict]:
    ...

from typing import Optional

def find_user(user_id: int) -> Optional[dict]:
    """根据用户ID查找用户，找不到返回None"""
    users = {
        1: {"name": "Alice", "age": 30},
        2: {"name": "Bob", "age": 25},
        3: {"name": "Charlie", "age": 35}
    }
    return users.get(user_id)

# 查找存在的用户
user = find_user(1)
if user is not None:
    print(f"找到用户: {user}")
else:
    print("用户不存在")

# 查找不存在的用户
missing = find_user(999)
print(f"查找结果: {missing}")

找到用户: {'name': 'Alice', 'age': 30}
查找结果: None

from typing import Optional

def create_greeting(name: str, title: Optional[str] = None) -> str:
    """创建问候语，title可选"""
    if title is not None:
        return f"Hello, {title} {name}!"
    return f"Hello, {name}!"

# 不带title
greeting1 = create_greeting("Alice")
print(greeting1)

# 带title
greeting2 = create_greeting("Alice", "Dr.")
print(greeting2)

# 显式传None
greeting3 = create_greeting("Bob", None)
print(greeting3)

Hello, Alice!
Hello, Dr. Alice!
Hello, Bob!

from typing import Optional, List

class ConfigManager:
    """配置管理器"""

    def __init__(self) -> None:
        self._config: dict = {
            "host": "localhost",
            "port": 8080,
            "debug": False
        }

    def get(self, key: str) -> Optional[str]:
        """获取配置值，不存在返回None"""
        return self._config.get(key)

    def get_with_default(self, key: str, default: Optional[str] = None) -> Optional[str]:
        """获取配置值，支持默认值"""
        value = self._config.get(key)
        if value is not None:
            return str(value)
        return default

    def get_required(self, key: str) -> str:
        """获取必需的配置值，不存在则抛出异常"""
        value = self._config.get(key)
        if value is None:
            raise KeyError(f"缺少必需的配置项: {key}")
        return str(value)

# 使用配置管理器
manager = ConfigManager()

host = manager.get("host")
print(f"host: {host}")

missing = manager.get("database")
print(f"database: {missing}")

with_default = manager.get_with_default("database", "sqlite:///default.db")
print(f"database (带默认值): {with_default}")

required = manager.get_required("port")
print(f"port (必需): {required}")

host: localhost
database: None
database (带默认值): sqlite:///default.db
port (必需): 8080