python iter()与 __iter__()的区别

Iterable 凡是可以for循环的 都属于 iterable 可迭代对象
Iterator 凡是可以next（)的 都是iterator 迭代器
可迭代对象(iterble)并不一定是 迭代器(iterator)

from collections import Iterable,Iterator
xxx='abcdec'   #字符串是可迭代对象
print isinstance(xxx,Iterable)
print isinstance(xxx,Iterator)

it_xxx = iter(xxx) #转换为迭代器
print isinstance(it_xxx,Iterable)
print isinstance(it_xxx,Iterator)

True
False

True
True

from collections import Iterable,Iterator
class A(object):
    def __init__(self,num):
        self.num = num
        self.start_num = -1

    def __iter__(self):
        return self

    def next(self):
        self.start_num += 1
        if self.start_num > self.num:
            raise StopIteration
        return  self.start_num

# iter()
b = [1,2,3]
it_b = iter(b)
print next(it_b)
print next(it_b)

# __iter__()
a = A(10)
print next(a)
print next(a)

print isinstance(it_b,Iterator)
print isinstance(a,Iterator)

#运行结果
1
2
0
1
True
True

True