处理None和with语句的Pythonic方法

value = some_function()  # 假设这个函数可能返回None
if value is not None:
    print(value.some_attribute)
else:
    print("Value is None")

from typing import Optional

def some_function() -> Optional[SomeClass]:
    # ...

class MyContextManager:
    def __enter__(self):
        # 打开资源
        return self

    def __exit__(self, exc_type, exc_value, traceback):
        # 清理资源
        pass

from contextlib import contextmanager

@contextmanager
def managed_resource(*args, **kwds):
    # 打开资源
    try:
        yield
    finally:
        # 清理资源
        pass

# 使用None的示例
def get_user_name(user_id):
    # 假设这个函数从数据库获取用户名，如果没有找到则返回None
    user = find_user_in_database(user_id)
    return user.name if user is not None else None

# 使用with语句的示例
class FileManager:
    def __init__(self, filename, mode):
        self.filename = filename
        self.mode = mode

    def __enter__(self):
        self.file = open(self.filename, self.mode)
        return self.file

    def __exit__(self, exc_type, exc_value, traceback):
        self.file.close()

# 使用with语句打开文件
with FileManager('example.txt', 'r') as file:
    content = file.read()
    print(content)