Python__getattr__、__setattr__、__delattr__、__getitem__、__setitem__、__getattribute__方法的理解

1. __getattr__(self, item):

在访问对象的item属性的时候，如果对象并没有这个相应的属性，方法，那么将会调用这个方法来处理。。。这里要注意的时，假如一个对象叫fjs,  他有一个属性：fjs.name = "fjs"，那么在访问fjs.name的时候因为当前对象有这个属性，那么将不会调用__getattr__()方法，而是直接返回了拥有的name属性了

2. __setattr__(self, item, value):

当试图对象的item特性赋值的时候将会被调用。

# -*- coding:utf-8 -*-
class Student:
    def __init__(self, work, score):
        self.work = work
        self.score = score
    def __getattr__(self, item):
        return item + ' is not exits'
 
    def __setattr__(self, key, value):
        self.__dict__[key] = value
        #object.__setattr__(self, key, value)  两条语句等效
    def __delattr__(self, name):
        print("你正在删除一个属性")
        return super().__delattr__(name)
    def __getitem__(self, item):
        return self.__dict__[item]
 
    def __setitem__(self, key, value):
        self.__dict__[key] = value
 
 
s = Student()
print(s.name)  # 调用__getattr__方法 输出'name is not exits'
s.age = 1  # 调用__setattr__ 方法
print(s.age)  # 输出 1
print(s['age'])  # 调用 __getitem__方法 输出1
s['name'] = 'tom'  # 调用 __setitem__ 方法
print(s['name'])  # 调用 __getitem__ 方法 输出 'tom'

del s.work # 调用__delattr__方法
try:
    print(s.work)    # 输出 'MyClass' object has no attribute 'work'
except AttributeError as reason:
    print(reason)          

输出结果为：

name is not exits
1
1
tom

3. __getattribute__

class C(object):
    a = 'abc'
    def __getattribute__(self, *args, **kwargs):
        print("__getattribute__() is called")
        return object.__getattribute__(self, *args, **kwargs)
#        return "haha"
    def __getattr__(self, name):
        print("__getattr__() is called ")
        return name + " from getattr"
    
    def __get__(self, instance, owner):
        print("__get__() is called", instance, owner)
        return self
    
    def foo(self, x):
        print(x)

class C2(object):
    d = C()
if __name__ == '__main__':
    c = C()
    c2 = C2()
    print(c.a)
    print(c.zzzzzzzz)
    c2.d
    print(c2.d.a)

 输出结果

__getattribute__() is called
abc
__getattribute__() is called
__getattr__() is called 
zzzzzzzz from getattr
__get__() is called <__main__.C2 object at 0x16d2310> <class '__main__.C2'>
__get__() is called <__main__.C2 object at 0x16d2310> <class '__main__.C2'>
__getattribute__() is called
abc