1 Iterable，可迭代：

一个类实现了iter()函数，则这个类是可迭代的，通常iter()函数必须返回一个
实现了next()的类的对象，当然如果自己实现了next()，也可以返回自己

2 Iterator 迭代器：

同时实现了iter()和next()的对象，就是迭代器

class Student():
    def __init__(self,name):
        self.name=name
        self.start=0
    def __iter__(self):
        return self
    def __next__(self):
        if self.start <len(self.name):
            result=self.name[self.start]
            self.start+=1
            return result
        else:
            raise StopIteration
s=Student("Jack Macial")
for elem in s:
    print(elem)

执行结果如下：

J
a
c
k
M
a
c
i
a
l

下面查看next函数的使用

class Student():
    def __init__(self,name):
        self.name=name
        self.start=0
    def __iter__(self):
        return self
    def __next__(self):
        if self.start <len(self.name):
            result=self.name[self.start]
            self.start+=1
            return result
        else:
            raise StopIteration
s=Student("Jack Macial")
print(next(s))
print(next(s))
print(next(s))
print(next(s))
print(next(s))
print(next(s))
print(next(s))
print(next(s))
print(next(s))
print(next(s))
print(next(s))
print(next(s))

执行结果如下：

J
a
c
k
M
a
c
i
a
l
Traceback (most recent call last):
  File "G:/python_flask/test.py", line 29, in <module>
    print(next(s))
  File "G:/python_flask/test.py", line 15, in __next__
    raise StopIteration
StopIteration