浅谈Python中的可迭代对象、迭代器、For循环工作机制、生成器

from collections import Iterable
from collections import Iterator
print isinstance(iter([1,2]),Iterator)
print isinstance(iter([1,2]),Iterable)
print isinstance([1,2],Iterator)
print isinstance([1,2],Iterable)
##result
True
True
False
True
##id可以查看一个对象在内存中的地址
test=[1,2,3]
testIter=iter(test)
print id(testIter)
print id(testIter)
print id(iter(test))
print id(iter(test))
print id(test.__iter__())
print id(test.__iter__())
##result:可迭代对象每次调用iter方法都会返回一个新的迭代器对象，而迭代器对象调用iter方法返回自身
67162576 
67162576 
67162688 
67162632 
67162856 
67163024

from collections import Iterable, Iterator
class Student(object):
 def __init__(self,score):
 self.score=score
 def __iter__(self):
 return iter(self.score)
 
test= Student([80,90,95])
print isinstance(test, Iterable)
print isinstance(test, Iterator)
for i in test:
 print i
##result
True
False
80
90
95
##可重复遍历
for i in test:
 print i
##result
80
90
95

print isinstance(iter(test),Iterator)
testIter=iter(test)
print testIter.next()
print testIter.next()
print testIter.next()
##result
True
80
90
95
##一旦取完了可迭代对象中所有的元素，再次调用next就会发生异常
print testIter.next()
##result
StopIteration: 

class Student(object):
 def __init__(self,score):
 self.score=score
 def __iter__(self):
 return self
 
 def next(self):
 if self.score<100:
 self.score+=1
 return self.score
 else:
 raise StopIteration()
 
test= Student(90)
print isinstance(test, Iterable)
print isinstance(test, Iterator)
print test.next()
print test.next()
print test.next()
for i in test:
 print i
##result
True
True
91
92
93
94
95
96
97
98
99
100
##如果此时再对test这个迭代器调用next方法，就会抛出异常
test.next()
##result
StopIteration: 

from collections import Iterable, Iterator
class Student(object):
 def __init__(self,score):
 self.score=score
 def __getitem__(self,n):
 return self.score[n]
 
test= Student([80,90,95])
print isinstance(test, Iterable)
print isinstance(test, Iterator)
print isinstance(iter(test), Iterable)
print isinstance(iter(test), Iterator)
for i in test:
 print i
##result
False
False
True
True
80
90
95
for i in range(0,3):
 print test[i]
##result
80
90
95
for i in iter(test):
 print i
##result
80
90
95