属性控制

1.__slots__控制属性访问

class MyClass:
    __slots__ = ('attr1', 'attr2')

    def __init__(self):
        self.attr1 = 10
        self.attr2 = 20
# 尝试添加不在 __slots__ 中的属性会报错
obj = MyClass()
obj.attr3 = 30  # 会引发 AttributeError

class Employee:
    __slots__ = ('name', 'id', 'department')

    def __init__(self, name, id, department):
        self.name = name
        self.id = id
        self.department = department

# 创建多个员工实例，节省内存
employees = [Employee('John', 1, 'HR'), Employee('Alice', 2, 'Finance')]

# 数据类（dataclass）：结合 __slots__ 可以更高效地定义具有固定属性的数据类。
from dataclasses import dataclass
@dataclass(slots=True)
class Point:
    x: int
    y: int

# 内存视图（memoryview）：用于高效地操作内存缓冲区，可与 __slots__ 一起优化内存使用
import array
class MyArray:
    __slots__ = ('data',)

    def __init__(self):
        self.data = array.array('i')
    def append(self, value):
        self.data.append(value)
arr = MyArray()
arr.append(1)

2.使用@property装饰器来实现属性的访问控制

class MyClass:
    def __init__(self):
        self._value = 0
    @property
    def value(self):
        return self._value

    @value.setter
    def value(self, new_value):
        if new_value >= 0:
            self._value = new_value
        else:
            raise ValueError("Value must be non-negative")
obj = MyClass()
print(obj.value)  
obj.value = 5
print(obj.value)  
# 尝试设置负数值会引发 ValueError
# obj.value = -1

class Person:
    def __init__(self, age):
        self.age = age

    @property
    def age(self):
        return self._age

    @age.setter
    def age(self, value):
        if not 0 <= value <= 120:
            raise ValueError("Age must be between 0 and 120")
        self._age = value
p = Person(11)
p.age = 22

3.使用描述符（ Descriptor ）：更高级的属性控制方式

class MyDescriptor:
    def __get__(self, instance, owner):
        print("Getting descriptor")
        return "Default value"

    def __set__(self, instance, value):
        print(f"Setting descriptor to {value}")

class MyClass:
    attribute = MyDescriptor()

my_instance = MyClass()
# 获取属性值，触发 __get__ 方法
print(my_instance.attribute)  
# 设置属性值，触发 __set__ 方法
my_instance.attribute = "New value"  

class ConfigValue:
    def __init__(self, min_value, max_value):
        self.min_value = min_value
        self.max_value = max_value

    def __get__(self, instance, owner):
        return instance.__dict__[self.name]

    def __set__(self, instance, value):
        if not self.min_value <= value <= self.max_value:
            raise ValueError(f"Value must be between {self.min_value} and {self.max_value}")
        instance.__dict__[self.name] = value

class Config:
    temperature = ConfigValue(0, 100)

config = Config()
# 设置有效的值
config.temperature = 50  
# 尝试设置无效的值，会触发异常
config.temperature = 150  

4.元类（ Metaclass ）：在类创建时控制属性的定义

class Meta(type):
    def __new__(cls, name, bases, attrs):
        if 'special_attribute' not in attrs:
            attrs['special_attribute'] = 'Default value'
        return super().__new__(cls, name, bases, attrs)

class MyClass(metaclass=Meta):
    pass

class DescriptorMeta(type):
    def __new__(cls, name, bases, attrs):
        for key, value in attrs.items():
            if hasattr(value, '__get__') and hasattr(value, '__set__'):
                attrs[key] = value
        return super().__new__(cls, name, bases, attrs)
class MyClass(metaclass=DescriptorMeta):
    attribute = MyDescriptor()