迭代器和可迭代对象

from collections import Iterable, Iterator


class ClassIterator:
    """迭代器必须实现__iter__和__next__方法，故迭代器一定是可迭代对象"""
    def __init__(self, obj):
        self.obj = obj
        self.position = 0

    def __iter__(self):
        pass

    def __next__(self):
        if self.position < len(self.obj.names):
            next_value = self.obj.names[self.position]
            self.position += 1
            return next_value
        else:
            raise StopIteration


class ClassMate:
    """只要实现了__iter__方法就是可迭代对象，可迭代对象返回一个迭代器"""
    def __init__(self):
        self.names = ["zhang san", "li si", "wang wu"]

    def __iter__(self):
        return ClassIterator(self)


classmate = ClassMate()
class_iterator = ClassIterator(classmate)

print(isinstance(classmate, Iterable))  # 返回True，因为实现了__iter__方法，所以是可迭代对象
print(isinstance(classmate, Iterator))  # 返回false，因为没有实现__next__方法，所以不是迭代器
print(isinstance(class_iterator, Iterable))  # 返回True，实现了__iter__
print(isinstance(class_iterator, Iterator))  # 返回True，实现了__iter__和__next__

"""for语句首先用iter(classmate)获取一个迭代器，然后用next(迭代器)逐个获取元素，直到捕捉到StopIteration"""
for i in classmate:
    print(i)

class ClassMate:
    def __init__(self):
        self.names = ["zhang san", "li si", "wang wu"]
        self.position = 0

    def __iter__(self): # 本身是一个迭代器
        return self

    def __next__(self):
        if self.position < len(self.names):
            next_value = self.names[self.position]
            self.position += 1
            return next_value
        else:
            raise StopIteration


classmate = ClassMate()

for i in classmate:
    print(i)