Detailed explanation of examples of python iterators

The object that can be directly used in the for loop is called iterable object (iterable);

The object that can be called by the next() function and continuously returns the next value is called iterator (iterator);

All iterable objects can be converted into iterators through the built-in function iter().

When using a for loop, the program will automatically call the iterator object of the object to be processed, and then use its next() method until a stoplteration exception is detected.

>>> l = [4,5,6,7,8,9,0]   #这是一个列表
>>> i = iter(l)                 #可迭代对象转换为迭代器；
>>> next(i)
4
>>> next(i)
5
>>> next(i)
6
>>> next(i)
7
>>> next(i)
8
>>> next(i)
9
>>> next(i)
0
>>> next(i)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration

Because there are no numbers exceeding 0 in the list, when the range exceeds, a StopIteration exception will be returned.

How to judge in a production environment

>>> L = [4,5,6]
>>> I = L.__iter__()
>>> L.__next__()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: &#39;list&#39; object has no attribute &#39;__next__&#39;
>>> I.__next__()
4
>>> from collections import Iterator, Iterable
>>> isinstance(L, Iterable)
True
>>> isinstance(L, Iterator)
False
>>> isinstance(I, Iterable)
True
>>> isinstance(I, Iterator)
True
>>> [x**2 for x in I]    
[25, 36]

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