freeCodeCamp/guide/english/python/iterators/index.md

title
Python Iterators

Python supports a concept of iteration over containers. This is implemented using two distinct methods; these are used to allow user-defined classes to support iteration.

Python Docs - Iterator Types

Iteration is the process of programatically repeating a step a given number of times. A programmer can make use of iteration to perform the same operation on every item in a collection of data, for example printing out every item in a list.

• Objects can implement a __iter__() method that returns an iterator object to support iteration.

• Iterator objects must implement:

  • __iter__(): returns the iterator object.

  • __next__(): returns the next object of the container.

  iterator_object = 'abc'.iter() print(iterator_object) print(id(iterator_object)) print(id(iterator_object.iter())) # Returns the iterator itself. print(iterator_object.next()) # Returns 1st object and advances iterator. print(iterator_object.next()) # Returns 2nd object and advances iterator. print(iterator_object.next()) # Returns 3rd object and advances iterator. print(iterator_object.next()) # Raises StopIteration Exception.

Output :

<str_iterator object at 0x102e196a0>
4343305888
4343305888
a
b
c
---------------------------------------------------------------------------
StopIteration                             Traceback (most recent call last)
<ipython-input-1-d466eea8c1b0> in <module>()
      6 print(iterator_object.__next__())     # Returns 2nd object and advances iterator.
      7 print(iterator_object.__next__())     # Returns 3rd object and advances iterator.
----> 8 print(iterator_object.__next__())     # Raises StopIteration Exception.

StopIteration: