def filter_multi(items,key=None):
 """
 可迭代对象去重(保持顺序不变)
 [1,4,7,2,4,7,3,5] ==> [1,4,7,2,3,5]
 """
 its = list()
 for x in items:
 val = x if key is None else key(x)
 if val not in its:
 yield val
 its.append(val)

#如:
print list(filter_multi([1,3,5,3,7,2,4,2]))
 
items = [{'a':1,'b':2},{'a':3,'b':4},{'a':1,'b':2},{'a':5,'b':6}]
print list(filter_multi(items,key=lambda k:(k['a'],k['b'])))

> s = "dasda"
> s.__iter__()
<str_iterator object at 0x7f23ebc44470>

> from collections import Iterable
> isinstance(s,Iterable)
True 

> s = [1,2,3,4,5]
> s.__next__()
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
AttributeError: 'list' object has no attribute '__next__'
> s = iter(s)
> type(s)
<class 'list_iterator'>
> s.__next__()
1
> from collections import Iterator
> isinstance(s,Iterator)
True

#coding=utf-8
from collections import Iterable,Iterator

class A:#只有__next__方法。不是迭代器也不是可迭代对象
 def __init__(self,start,end):
  self.start = start
  self.end = end

 def __next__(self):
  if self.start < self.end:
   i = self.start
   self.start += 1
   return i
  else:
   raise StopIteration()

class B:#只有__iter__方法，__iter__返回的是一个没有__next__的对象。是可迭代对象，不是迭代器
 def __init__(self,start,end):
  self.start = start
  self.end = end

 def __iter__(self):
  return self

class C:#只有__iter__方法，__iter__返回的是一个有__next__的对象。是可迭代对象，不是迭代器
 def __init__(self,start,end):
  self.start = start
  self.end = end

 def __iter__(self):
  return A(self.start,self.end)

class D:#既有__iter__又有__next__，__iter__返回的是自身，有__next__的对象，是迭代器和可迭代对象
 def __init__(self,start,end):
  self.start = start
  self.end = end

 def __iter__(self):
  return self

 def __next__(self):
  if self.start < self.end:
   i = self.start
   self.start += 1
   return i
  else:
   raise StopIteration()

class E:#既有__iter__又有__next__，__iter__返回的不是自身，有__next__的对象，是迭代器和可迭代对象
 def __init__(self,start,end):
  self.start = start
  self.end = end

 def __iter__(self):
  return A(self.start,self.end)

 def __next__(self):
  if self.start < self.end:
   i = self.start
   self.start += 1
   return i
  else:
   raise StopIteration()

class F:#既有__iter__又有__next__，__iter__返回的是没有__next__的对象，是迭代器和可迭代对象
 def __init__(self,start,end):
  self.start = start
  self.end = end

 def __iter__(self):
  return 1

 def __next__(self):
  if self.start < self.end:
   i = self.start
   self.start += 1
   return i
  else:
   raise StopIteration()

s = A(5,10)
print('Iterable:',isinstance(s,Iterable))
print('Iterator:',isinstance(s,Iterator))

s = B(5,10)
print('Iterable:',isinstance(s,Iterable))
print('Iterator:',isinstance(s,Iterator))

s = C(5,10)
print('Iterable:',isinstance(s,Iterable))
print('Iterator:',isinstance(s,Iterator))

s = D(5,10)
print('Iterable:',isinstance(s,Iterable))
print('Iterator:',isinstance(s,Iterator))


s = E(5,10)
print('Iterable:',isinstance(s,Iterable))
print('Iterator:',isinstance(s,Iterator))

s = F(5,10)
print('Iterable:',isinstance(s,Iterable))
print('Iterator:',isinstance(s,Iterator))

Iterable: False
Iterator: False

Iterable: True
Iterator: False

Iterable: True
Iterator: False

Iterable: True
Iterator: True

Iterable: True
Iterator: True

Iterable: True
Iterator: True

s = A(1,4)
for i in s:
 print(i)

->

Traceback (most recent call last):
 File "IteratorZZ.py", line 68, in <module>
 for i in s:
TypeError: 'A' object is not iterable
#提示并非一个可迭代对象

s = B(1,4)
print('Iterable:',isinstance(s,Iterable))
print('Iterator:',isinstance(s,Iterator))
for i in s:
 print(i)

->

Iterable: True
Iterator: False
Traceback (most recent call last):
 File "IteratorZZ.py", line 75, in <module>
 for i in s:
TypeError: iter() returned non-iterator of type 'B'
#提示__iter__()返回的不是一个迭代器

s = C(1,4)
print('Iterable:',isinstance(s,Iterable))
print('Iterator:',isinstance(s,Iterator))
for i in s:
 print(i)

->

Iterable: True
Iterator: False
1
2
3
#成功

s = D(1,4)
print('Iterable:',isinstance(s,Iterable))
print('Iterator:',isinstance(s,Iterator))
for i in s:
 print(i)

->

Iterable: True
Iterator: True
1
2
3
#成功

s = E(1,4)
print('Iterable:',isinstance(s,Iterable))
print('Iterator:',isinstance(s,Iterator))
for i in s:
 print(i)

->

Iterable: True
Iterator: True
1
2
3
#成功

s = F(1,4)
print('Iterable:',isinstance(s,Iterable))
print('Iterator:',isinstance(s,Iterator))
for i in s:
 print(i)

->
Iterable: True
Iterator: True
Traceback (most recent call last):
 File "IteratorZZ.py", line 115, in <module>
 for i in s:
TypeError: iter() returned non-iterator of type 'int'
#失败，__iter__返回的不是迭代器