python12——包装标准类

#包装
class List_feng(list):
    def show_midle(self):
        mid_index = int(len(self)/2)
        return self[mid_index]

l1 = List_feng('helloworld')
print(l1)
print(l1.show_midle())
#授权
class Open:
    def __init__(self,filename,mode='r',encoding='utf-8'):
        self.file = open(filename,mode,encoding=encoding)
        # self.mode = mode
        # self.encoding = encoding
    #此时无法进行写入
    def write(self):
        pass
    def __getattr__(self, item):
        print(item,type(item))
        return getattr(self.file,item)
f1 = Open('a.txt','w')
print(f1.file)
print(f1.read)

class Feng:
    pass
f1 = Feng()
#是否被实例
print(isinstance(f1,Feng))

class Sub_feng(Feng):
    def __getattr__(self, item):
        print('执行了1111111')
    #都会触发
    def __getattribute__(self, item):
        print('执行了22222')
        raise AttributeError('抛出异常了')

print(issubclass(Sub_feng,Feng))

item系列

class Feng:
    def __getitem__(self, item):
        print('getitem')
        return self.__dict__[item]
    def __setitem__(self, key, value):
        print('setitem')
        self.__dict__[key]=value
    def __delitem__(self, key):
        print('delitem')
        self.__dict__.pop(key)
f1 = Feng()
#f1.name = 'fengfeng'
f1['name']='fengfeng'
print(f1.__dict__)
print(f1['name'])
del f1['name']
print(f1.__dict__)

Str 和 Repr

l = list('hello')
print(l)

class Feng:
    def __str__(self):
        return '自定义显示方式'
    def __repr__(self):
        return 'repr__________'
f1 = Feng()
print(f1)