可迭代对象与迭代器

可迭代协议：可迭代对象必须包含__iter__方法，并且返回一个的迭代器。
满足可迭代协议的对象称为可迭代对象。可迭代对象即可使用for …… in的对象。
迭代协议：满足迭代协议的对象时迭代器。

1. 包含__iter__方法，并且该方法返回迭代器本身
2. 包含__next__方法，调用该方法返回下一个值，当没有值可返回时，抛出StopIteration异常终止迭代。

from collections.abc import Iterable, Iterator
class Iter_obj:
    def __init__(self, n) -> None:
        self.n = n
        self.data = [i for i in range(n)]
    def __iter__(self):
        """返回一个迭代器"""
        return iter(self.data)  # list时可迭代对象但不是可迭代器，
        # 基本数据类型的容器类型都是可迭代对象，但都不是迭代器

class Iterator_:
    def __init__(self, n):
        self.n = n 
        self.start = 0

    def __iter__(self):
        """返回一个迭代器"""
        return self  # 实现了__iter__和__next__方法的对象就是迭代器，所以返回本身
    
    def __next__(self):
        if self.n>self.start:
            self.start+=1
            return self.start
        else:
            raise StopIteration()


if __name__ == "__main__":
    iter_obj = Iter_obj(3)
    print(isinstance(iter_obj, Iterable))
    for x in iter_obj:  # 可迭代对象可以使用for in语句
        print(x)
    iterator_ = Iterator_(5)
    print(isinstance(iterator_, Iterator))
    for x in Iterator_(5):
        print(x)
    

iter方法和next方法

iter方法调用对象的__iter__方法返回一个迭代器。
next方法调用对象的__next__方法返回下一条数据
list、tuple、set、dict都可以使用iter方法得到对应的迭代器，然后可以使用next方法获取下一条数据。

from collections.abc import Iterator, Iterable

def iterable_to_iterator(obj):
    print('-'*20)
    s = type(obj)
    print("%s is Iterable: %s"%(s, isinstance(obj, Iterable)))
    print("%s is Iterator: %s"%(s, isinstance(obj, Iterator)))
    
    try:
        iterator = iter(obj)
        print("%s is Iterator: %s"%(iterator, isinstance(iterator, Iterator)))
        while True:
            print(next(iterator))
    except StopIteration as e:
        pass 
    finally:
        print('-'*20)


if __name__ == "__main__":
    string = "python"
    mylist = ['a', 'b', 'c']
    myset = set([1,2,3])
    mydict =  dict(zip(myset, mylist))
    for obj in [string, mylist, myset, mydict]:
        iterable_to_iterator(obj)

常见可迭代器与可迭代对象

from collections.abc import Iterator, Iterable

def iterable_or_iterator(obj):
    
    s = type(obj)
    print("%s is Iterable: %s"%(s, isinstance(obj, Iterable)))
    print("%s is Iterator: %s\n"%(s, isinstance(obj, Iterator)))

if __name__ == "__main__":
    zip_ = zip([1,2],[3,4])
    dic = dict(zip_)
    map_ = map(int, ['1','2'])
    enumerate_ = enumerate(['a','b','c'])
    for obj in [list(), tuple(), set(), dict(), str(), range(3), zip_,map_, enumerate_,
                dic.keys(), dic.values(), dic.items()]:
        iterable_or_iterator(obj)
    
# <class 'list'> is Iterable: True
# <class 'list'> is Iterator: False

# <class 'tuple'> is Iterable: True
# <class 'tuple'> is Iterator: False

# <class 'set'> is Iterable: True
# <class 'set'> is Iterator: False

# <class 'dict'> is Iterable: True
# <class 'dict'> is Iterator: False

# <class 'str'> is Iterable: True
# <class 'str'> is Iterator: False

# <class 'range'> is Iterable: True
# <class 'range'> is Iterator: False

# <class 'zip'> is Iterable: True
# <class 'zip'> is Iterator: True

# <class 'map'> is Iterable: True
# <class 'map'> is Iterator: True

# <class 'enumerate'> is Iterable: True
# <class 'enumerate'> is Iterator: True

# <class 'dict_keys'> is Iterable: True
# <class 'dict_keys'> is Iterator: False

# <class 'dict_values'> is Iterable: True
# <class 'dict_values'> is Iterator: False

# <class 'dict_items'> is Iterable: True
# <class 'dict_items'> is Iterator: False

zip、map、enumerate的返回值是迭代器，dict的keys、values、items的返回值和range的返回值都是可迭代对象，基本数据类型的list、tuple、set、dict、string都是可迭代对象

标签：__,obj,迭代,Iterator,对象,True,Iterable
来源： https://www.cnblogs.com/baiyutang7/p/16407102.html