Python Iterator Tutorial

This tutorial was built using Python 3.6

In this tutorial we’ll be looking at what iterators are with Python. We’ll also be looking at how we can effectively work with them and improve our Python programs using them.

What Are Iterators?

Iterators are cool in the sense that they allow us to step over every item in an array, object or file and perform work on each item. For example, we could take the string test and use an iterator to step over every character element within that string.

>>> string = "test"

>>> for character in string:
>>>    print(character)

## Output
t
e
s
t

Iterables

Iterables in Python represent something that we can actively iterate over. These are things like lists, sets and even strings as we’ve seen in the previous demonstration. If we wish to turn an iterable into an iterator then we can use the iter built in function which takes in the iterable like so:

>>> string = "test"
>>> iterator = iter(string)
>>> iterator = iter(string)
>>> print(iterator.next())
t
>>> print(iterator.next())
e
>>> print(iterator.next())
s
>>> print(iterator.next())
t

The next() Method

When we have an iterator object we can effectively step through it using the next() method. This will simply return the next element of the given iterator object, if no further elements exist in the iterator then a StopIteration exception will be raised:

>>> iterator = iter(string)
>>> print(iterator.next())
t
>>> print(iterator.next())
e
>>> print(iterator.next())
s
>>> print(iterator.next())
t
>>> print(iterator.next())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration

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