迭代器 Iterator

1.自定义迭代器

# 迭代器
# 自定义迭代器

# Iterable ：判断对象是否为迭代对象
# Iterator : 判断对象是否是迭代器
from collections.abc import Iterable
from collections.abc import Iterator

class List(object):

    def __init__(self):
        self.items=[]
        pass
    def __iter__(self):
        return listIterator()

    def add(self,item):
        self.items.append(item)
        pass

class listIterator(object):
    def __init__(self):
        pass
    def __iter__(self):
        pass
    def __next__(self):
        print("__next__")
        pass

list=List()
list.add(1)
list.add(2)
iter_list=iter(list)
print(isinstance(list,Iterable)) # 判断是否是可迭代对象
print(isinstance(iter_list,Iterator)) #判断是否是迭代器

print(next(iter_list))


输出：
True
True
__next__
None

Process finished with exit code 0

自定义一个迭代器

# 自定义一个迭代器

class List(object):
    def __init__(self):
        self.items=[]
        self.current=0
        pass

    def __iter__(self):
        return  self

    def __next__(self):
        print("__next__")
        if self.current<len(self.items):
            item=self.items[self.current]
            self.current+=1
            return item
        else:
            self.current = 0
            raise  StopIteration  #抛出异常
        # return 200
        pass
    def add(self, other):
        self.items.append(other)
        pass

if __name__=="__main__":
    print("main")
    list=List()
    list.add(1)
    list.add(2)

    iter_list=iter(list)
    # print(next(iter_list))

    for t in iter_list:
        print(t)



    for t in iter_list:
        print(t)

3. for...in...循环的本质

1. 先调用iter()函数，它会自动调用可迭代对象中的__iter__方法，此方法返回这个可迭代对象的 迭代器对象
2. 对获取到的迭代器不断调用next()函数，它会自动调用迭代器中的__next__方法来获取下一个值
3. 当遇到StopIteration异常后循环结束

# 练习

class LIST(object):
    def __init__(self):
        self.items=[]
        self.current=0
        pass

    def __iter__(self):
        return self
        pass

    def __next__(self):
        if self.current<len(self.items):
            item=self.items[self.current]
            self.current+=1
            return item
        else:
            self.current=0
            raise StopIteration
        pass

    def add(self,other):
        self.items.append(other)
        pass


if __name__=="__main__":
    my_list=LIST()
    my_list.add(1)
    my_list.add(2)

    iter_list=iter(my_list)

    # for i in iter_list:
    #     print(i)
    #
    # for i in iter_list:
    #     print(i)
    tmp=list(my_list)
    print(tmp)

    tmp1=tuple(my_list)
    print(tmp1)

2023-04-25