Python iterator protocol and iterative object, iterator object

One, the iterator protocol definition:

Iteration: is a repeating process, each repetition, based on the last result

 whileTrue:#simple repetition.    Print('What are you talking about?') L=['a','b','C','D']count=0 whileCount <Len (l):Print(L[count]) Count+=1

An iterator protocol is an object that must provide a next method that either returns the next item in the iteration, or causes a Stopiteration exception to terminate the iteration (only backward cannot go forward)

Two, can iterate the object definition:

An object that implements an iterator protocol (how to: Define an __iter__ () method within an object) is a __iter__ method under an object: an object. __iter__, which is an iterative object

s='Hello'L=['a','b','C','D']t=('a','b','C','D') DiC={'name':'Egon','Sex':'m'," Age": 18}set1={1,2,3}f=open ('Db.txt') s.__iter__() L.__iter__() T.__iter__() dic.__iter__() Set1.__iter__() F.__iter__() The above is an iterative object

Third, the Iterator object definition:

An iterative object executes the built-in __iter__ method, resulting in an iterator object

1, there is __iter__, the execution gets still the iteration itself
2, there are __next__
3, not dependent on the index of the value method

dic={'name':'Egon','Sex':'m'," Age": 18}i=dic.__iter__()#print (i) #iterator迭代器#i.__next__ () #next (i)Print(Next (i))Print(Next (i))Print(Next (i))Print(Next (i))#stopiterationL=['a','b','C','D']i=l.__iter__()Print(Next (i))Print(Next (i))Print(Next (i))Print(Next (i))Print(Next (i))#stopiteration

Iv. Advantages of Iterator objects

1: Provides a unified (index-independent) iterative approach
2: The iterator itself, which saves memory more than other data types

l=['a','b','C','D']i=ITER (l) DIC={'a': 1,'b': 2}x=Dic.keys ()Print(x) I=x.__iter__() with open ('a.txt') as F:#print (Next (f))    #print (Next (f))    #print (Next (f))F.read ()

V. Disadvantages of Iterator objects

1: One-time, can only go backward, can not be returned, the index value is flexible
2: Cannot predict when the value end, that is, cannot predict the length

l=['a','b','C',' D ' ]i=iter (l)print(Next (i))print(next (i )) Print(Next (i))

Six, for loop and iterative objects

Anything that can be used for loops is an iterative object

l=['a','b','C',' D ' ]for in#iter_l=l.__iter__ ()    print( Item) for in {1,2,3,4}:    print(item)

Vii. judging an iterative object and an iterator object

Requires from collections import Iterable,iterator

Use one of the isinstance () to determine whether an iterator object is an iterative object

 fromCollectionsImportiterable,iterators='Hello'L=['a','b','C','D']t=('a','b','C','D') DiC={'name':'Egon','Sex':'m'," Age": 18}set1={1,2,3}f=open ('a.txt')#Judging an Iterative objectPrint(Isinstance (s,iterable))Print(Isinstance (l,iterable))Print(Isinstance (t,iterable))Print(Isinstance (dic,iterable))Print(Isinstance (set1,iterable))Print(Isinstance (f,iterable))#To determine the iterator objectPrint(Isinstance (s,iterator))Print(Isinstance (l,iterator))Print(Isinstance (t,iterator))Print(Isinstance (dic,iterator))Print(Isinstance (set1,iterator))Print(Isinstance (F,iterator))

Python iterator protocol and iterative object, iterator object