Python Iterator Vs Iterables

An Iterator is an Object which contains a countable number of values or elements. You can use this one to Traverse all those elements. The Python iterator uses the special methods called __iter__() and __next__() methods to traverse the object elements.

Python Iterator Vs Iterables

If we can get the iterators from it, then we call that object as iterable. So far, we have seen the objects called Lists, Tuples, Sets, and Dictionaries. From these objects, you can call Iter. This section explains how to use this Python class and create our own infinity iterators with practical examples.

String Iterator Example

In python, strings are iterable objects. Here, we use for loop to loop each character in a string and return that character. By default, or say, For loop implements the Iterator object concept without your knowledge.

stri = 'tutorialgateway'
 
for x in stri:
    print(x, end = '  ')

t u t o r i a l g a t e w a y

For loop Iterator Example

In this example, we used both for loop and this. In this programming languages, we have to use the next() function to return an element or value from an iterator.

Remember, the next() method returns one item at a time. So, for n number of items, you have to use n next() statements. Here, we used the next() for one time. So, it returns the first character from a string.

stng = 'tutorialgateway'
  
for x in stng:
     print(x, end = '  ')
  
print("\n**** Output *****")
itr = iter(stng)
  
print(next(itr))

t u t o r i a l g a t e w a y
**** Output *****
t

Let me use next() to traverse all the characters in a string. This time, iterators write the completed string.

sting = 'tutorialgateway'
 
for x in sting:
    print(x, end = '  ')
 
print("\n**** Example *****")
itr = iter(sting)
 
print(next(itr))
print(next(itr))
print(next(itr))
print(next(itr))
print(next(itr))
print(next(itr))
print(next(itr))
print(next(itr))

t u t o r i a l
**** Example *****
t
u
t
o
r
i
a
l

Python List Iterator example

In this example, we show how to traverse List items and print them.

numbers = [10, 20, 30, 40, 50]
 
itr = iter(numbers)
 
print(next(itr))
print(next(itr))
print(next(itr))
print(next(itr))
print(next(itr))

In this list example, we used the __next__() special method. If you observe the last statement, we are trying to return the next element that doesn’t exist. That’s why Iter is called StopIteration.

numbers = [10, 20, 30, 40, 50]
 
itr = iter(numbers)
 
print(itr.__next__())
print(itr.__next__())
print(itr.__next__())
print(itr.__next__())
print(itr.__next__())
print(itr.__next__())

Set Iterator Example

You can use this to traverse the set items and returns the object. This program traverses the numbers in a Set and prints each one of them.

mySet = {1, 2, 3, 4, 5}
 
ittr = iter(mySet)
 
print(ittr.__next__())
print(ittr.__next__())
print(ittr.__next__())
print(ittr.__next__())
print(ittr.__next__())

Tuple Example

The Python iterator object can also allow you to use it on Tuples as well. This program iterates Tuple items and prints each item in a tuple.

fruits = ('Apple', 'Orange', 'Grape', 'Banana', 'Kiwi')
 
fruit_itr = iter(fruits)
 
print(next(fruit_itr))
print(next(fruit_itr))
print(next(fruit_itr))
print(next(fruit_itr))
print(next(fruit_itr))

Apple
Orange
Grape
Banana
Kiwi

Create Own Iterator in Python

It is a simple class called Counter. In this example, first, we declared a maximum value within the __init__ method. The __iter__ method is to initialize the value of an iterable object. For now, we set the number to 0. It means Iter starts at 0.

The __next__ method is to select the next element from an Object. Within this method, we used the If Else Statement to check whether the next number is greater than the maximum value or not. If True, StopIteration error is raised. Otherwise, the number incremented.

class Counter:
 
    def __init__(self, maximum):
        self.maximum = maximum

    def __iter__(self):
        self.number = 0
        return self
 
    def __next__(self):
        number = self.number
 
        if number > self.maximum:
            raise StopIteration
        else:
            self.number = number + 1
            return number
 
numbers = Counter(10)
a = iter(numbers)

print(next(a))
print(next(a))
print(next(a))

The above code displays numbers from 0 to 2. It is because we used next(a) three times only. In this program, we used for loop to iterate the Counter class where the maximum value is 10. This prints the values from 0 to 10. __iter__() starts at 0, and __next__() print elements up to 10.

class Counter:
 
    def __init__(self, maximum):
        self.maximum = maximum
 
    def __iter__(self):
        self.number = 0
        return self
 
    def __next__(self):
        number = self.number
 
        if number > self.maximum:
            raise StopIteration
        else:
            self.number = number + 1
            return number
 
for t in Counter(10):
    print(t)

Infinity Iterator class

While you create your own iter, you should always be careful with Infinity loops. If you forget to raise the error, then you end up in infinity loops. It is a simple example of an infinity iterator object. It is the same as above, but we removed the If statement.

class Counter:
 
    def __iter__(self):
        self.number = 0
        return self

    def __next__(self):
        number = self.number

        self.number = number + 1
        return number
      
numbers = Counter()
a = iter(numbers)
 
print(next(a))
print(next(a))
print(next(a))

0
1
2

Although the above example is an infinite iter, you might not have noticed it. It is because we used the next() three times only. So, let me use for loop to Ian iter function the Counter class. Please refer to the Dictionary article.

class Counter:
 
    def __iter__(self):
        self.num = 0
        return self
 
    def __next__(self):
        num = self.num
 
        self.num = num + 1
        return num
     
for t in Counter():
    print(t)

Now you can see the infinity object. This executes continuously.