对象的属性访问
>>> # hasattr()用于判断对象中是否拥有某属性，getattr()用于获取对象中某属性的值，setattr()用于设置对象中某属性的值，delattr()用于删除对象中的某属性。与之相对应的有4个魔法方法，分别是__getattribute__()、__getattr__()、__setattr__()和__delattr__()>>> # 其中，__getattribute__()、__setattr__()和__delattr__()分别与getattr()、setattr()和delattr()相对应，而__getattr__()则是当用户试图获取一个不存在的属性时才会被触发的魔法方法，与getattr()貌合神离，不要搞错了。此外，无论访问的属性是否存在，__getattribute__()都会优先被触发；__setattr__()和__delattr__()看似普通不过的赋值或删除操作却可能会造成无限递归的“死亡螺旋”，只有使用super()或引入__dict__后再进行相应操作，曲线救国，方能安全实现。
>>> # hasattr()用于判断对象中是否拥有某属性
>>> class C:
... def __init__(self, name, age):
... self.name = name
... self.age = age
...
>>> c = C("小甲鱼", 18)
>>> hasattr(c, "name")
True
>>> # getattr()用于获取对象中某属性的值
>>> getattr(c, "name")
'小甲鱼'
>>> getattr(c, "age")
18
>>> # setattr()用于设置对象中某属性的值
>>> setattr(c, "_C__age", 19)
>>> getattr(c, "age")
18
>>> c.__dict__
{'name': '小甲鱼', 'age': 18, '_C__age': 19}
>>> getattr(c, "_C__age")
19
>>> # delattr()用于删除对象中的某属性
>>> delattr(c, "_C__age")
>>> getattr(c, "_C__age")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'C' object has no attribute '_C__age'
>>> c.__dict__
{'name': '小甲鱼', 'age': 18}
>>> #__getattribute__()：当获取属性时触发，对应getattr()
>>> class C:
... def __init__(self, name, age):
... self.name = name
... self.__age = age
... def __getattribute__(self, item):
... print("拿来吧你")
... return super().__getattribute__(item)
...
>>> c = C('小甲鱼', 18)
>>> print(getattr(c, 'name'))
拿来吧你
小甲鱼
>>> print(c._C__age)
拿来吧你
18
>>> try:
... c.Fishc
... except AttributeError as e:
... print(e)
...
拿来吧你
'C' object has no attribute 'Fishc'
>>> #__getattr__()：当试图获取一个不存在的属性时触发
>>> class C:
... def __init__(self, name, age):
... self.name = name
... self.__age = age
... def __getattribute__(self, item):
... print("拿来吧你")
... return super().__getattribute__(item)
... def __getattr__(self, item):
... if item == 'fishc':
... print('I love fishc')
... else:
... raise AtttributeError(item)
...
>>> c = C('小甲鱼', 18)
>>> try:
... c.x
... except AttributeError as e:
... print(e)
...
拿来吧你
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
File "<stdin>", line 12, in __getattr__
NameError: name 'AtttributeError' is not defined
>>> #__setattr__()当设置属性时触发，对应setattr()
>>> # class D:
>>> # def __setattr__(self, name, value):
>>> # self.name = value
>>> #
>>> # d = D()
>>> #d.name = '小甲鱼'#报错RecursionError: maximum recursion depth exceeded
>>> #捕获到赋值操作时，执行self.name = value，相当于又给自己调用了一次赋值操作，则会继续执行self.name = value，无限递归导致死循环
>>> class D:
... def __setattr__(self, name, value):
... self.__dict__ = value
...
>>> d = D()
>>> d.name = '小甲鱼'
>>> print(d.name)
小甲鱼
>>> #__delattr__()：当一个属性被删除时触发，对应delattr()
>>> class D:
... def __setattr__(self, name, value):
... self.__dict__ = value
... def __delattr__(self, item):
... del self.__dict__
...
>>> d= D()
>>> d.name = '小甲鱼'
>>> print(d.__dict__)
{'name': '小甲鱼'}
>>> del d.name
>>> print(d.__dict__)
{}
>>> {:7_141:}
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