TypeError: iter() returned non-iterator of type 'xx' 从Python3开始，要用__next__

从Python3开始，要用__next__

http://www.python.org/dev/peps/pep-3114/

代码：
class MyIterator(object):
    def __init__(self,step):
        self.step=step
    
    def next(self):
        if self.step==0:
            raise StopIteration
        self.step-=1
        return self.step
    
    def __iter__(self):
        return self
    
for el in MyIterator(5):
    print(el)
运行结果：
Traceback (most recent call last):
  File "..\pythonadvancedprogramming\advancedThree.py", line 19, in
    for el in MyIterator(5):
TypeError: iter() returned non-iterator of type 'MyIterator'

但是把 def next(self): 改为def __next__(self): 就没有问题了