Little knowledge , Great challenge ！ This article is participating in “ A programmer must have a little knowledge ” Creative activities

iterator

Iteration is a way to access collection elements . An iterator is an object that remembers the traversal position . The iterator object is accessed from the first element of the collection , Until all elements are accessed . Iterators can only go forward, not backward .

1. Iteratable object

python Some data types in the language can be used directly for Loop to get the element value , such as ：

Collection data type ：list,tuple,dict,set,str etc.

generator （generator）, Including generator and belt yield Of generator function

These can act directly on for Circular objects are collectively called iteratable objects ：Iterable

2. Decide if you can iterate

You can use isinstance() Function to determine whether an object is an iteratable object Iterable

>>> from collections import Iterable

>>> isinstance([],Iterable)
>>> True

>>> isinstance({},Iterable)
>>> True

>>> isinstance("abc",Iterable)
>>> True

>>> isinstance((x for x in range(10)),Iterable)
>>> True

>>> isinstance(100,Iterable)
>>> False
 Copy code 

We know that generators can not only use for Loop through to get the element , You can also use next() The function keeps calling to return the next value , Until the last throw StopIteration An error means that the next value cannot be returned .

3. iterator

Can be next() The object that function calls and returns the next value continuously is called an iterator ：Iterator.

use isinstance() Function to determine whether an object is an iterator object ：

>>> from collections import Iterator

>>> isinstance([],Iterator)
>>> False

>>> isinstance({},Iterator)
>>> False

>>> isinstance('abc',Iterator)
>>> False

>>> isinstance((x for x in range(10)),Iterator)
>>> True

>>> isinstance(100,Iterator)
>>> False
 Copy code 

From the above code, you can see the list , aggregate , Dictionaries , Although strings are iteratable objects, they are not iterators . The generator is both an iteratable object and an iterator .

4. iter() function

It says that all generators are Iterator. and list,dict,str Such iteratable objects are not Iterator, But we can pass iter() The function converts it to Iterator. as follows ：

>>> isinstance(iter([]),Iterator)
>>> True

>>> isinstance(iter({}),Iterator)
>>> True

>>> isinstance(iter('abc'),Iterator)
>>> True
 Copy code 

summary

• What works for The objects of the loop are all Iterable type
• Usually used as next() Function objects are Iterator type
• The collection data type is as follows list,dict,str Wait, although it is Iterable No Iterator, But through iter() Function to Iterator