Python Iterators(what,iter,next and example)

• The built-in function iter takes an iterable object and returns an iterator.
• Each time we call the next method on the iterator gives us the next element. 
• If there are no more elements, it raises a StopIteration.
• Iterators are implemented as classes. 
• Here is an iterator that works like built-in xrange function. 
• The __iter__ method is what makes an object iterable. 
• Behind the scenes, the iter function calls __iter__ method on the given object. 
• The return value of __iter__ is an iterator. 
• It should have a next method and raise StopIteration when there are no more elements.

>>> x = iter([1, 2, 3])

>>> x

<listiterator object at 0x1004ca850>

>>> x.next()

1

>>> x.next()

2

>>> x.next()

3

>>> x.next()

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

StopIteration