python 成员关系：__contains__,__iter__和__getitem__

#__contains__优于__iter__优于__getitem__方法
#__contains__方法应该把成员关系定义为对一个映射应用键（并且可以使用快速查找），以及用于序列的搜索

class Iters:
    def __init__(self, value):
        =value
    def __getitem__(self, i):   
        print('get[%s]:'%i, end=' ')
        return [i]

    def __iter__(self):
        print('iter=>', end=' ')
        =0
        return self

    def __next__(self):
        print('next:', end=' ')
        if ==len():
            raise StopIteration
        item=[]
        +=1
        return item

    def __contains__(self, x):    #in操作
        print('contains: ',end=' ')
        return x in

    
x=Iters([1,2,3,4,5])
print(3 in x)    #contains:  True
for i in x:
    print(i, end=', ')    #iter=> next: 1, next: 2, next: 3, next: 4, next: 5, next:
print()
print([i**2 for i in x])    #iter=> next: next: next: next: next: next: [1, 4, 9, 16, 25]
print(list(map(bin,x)))    #iter=> next: next: next: next: next: next: ['0b1', '0b10', '0b11', '0b100', '0b101']
i=iter(x)
while True:
    try:
        print(next(i), end=' @ ')    #iter=> next: 1 @ next: 2 @ next: 3 @ next: 4 @ next: 5 @ next:
    except StopIteration:
        break
print()   
print(x[0])    #get[0]: 1   __getitem__支持索引
print(x[:-1])    #get[slice(None, -1, None)]: [1, 2, 3, 4]