Everything You Need to Learn About Iterator in Python

What is an Iterator?

An iterator is an object that is used to iterate or loop through the elements or items in the collections such as List, Set, etc.

Iterator: the name came from iterating which is a technical term for looping the elements.

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What is an Iterator in Python?

An iterator is an object which is meant for the purpose in Python, is nothing but looping through iterable objects like lists, tuples, dicts, and sets.

Instantiating the Iterator in Python

The iterator consists of two methods: 

1. iter() and 
2. next().  

Iter() method is used to initialize the iterator object so that the instance of this object can be used for iterating.

Syntax is

myiterator = iter()

Iteration of the Iterator

The next() method is used to iterate over the iterable objects. The next() method returns the next value in the iterable object.

Syntax is

item = next(myiterator)

Iterator vs Iterable

In Python, the List, Tuple, Set, and Dict are all iterable objects. These iterable objects have an iter() method which is used to get an iterator. It also considered the string object an iterable object in Python.

Syntax is

tupleObj = (“Red”, “Orange”)

myiterator = iter(tupleObj)

print(next(myiterator))

Example 1

Here, you will look at how to return an iterator from the list and display the value using print().

Output

Example 2:

Here, you will look at how to return an iterator from the String object and display each value with print().

Output

Ok, and with that, you looked into what an Iterator is and what an Iterable Object is. Now, let us move on to loops.

Loop Through an Iterator on a Collection Object

Loop can be used to iterate through iterable objects.

Example 1:

In this example, you will see how to iterate over the list in Python. You will see 2 methods to iterate over a list in Python.  

Method 1: Using for loop

Output

Method 2: Using for loop and range()

Output

Example 2:

In this example, you will look at how to iterate over the tuple in Python. Here, you will be using for loop to iterate through tuple.

Output

Example 3:

In this example, you will see how to iterate over the String in Python.  You are going to use for loop in this example to iterate through String.

Output

Built-in Iterators in Python

There are some compelling built-in Iterators in Python, which will be very useful for the programmers for effective looping, and it also speeds up the code execution.   

These built-in iterators are available in the module ‘itertools’ in Python. This module implements several iterative building blocks.

Here are a few useful iterators in Python

accumulate(iter, func): 

This accumulate iterator will take two parameters. These two parameters are nothing but an iterable target and function, which will be followed at each iteration of value in target.

If the input iterable is empty, then the output iterable also will be empty. If no function is passed, addition takes place by default.

Output

Chain (iter1, iter2…):

Chain iterator function is used to print all the values in iterable one after another mentioned in the function parameters.

Output                                        

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Create an Iterator

In Python, you can create a class/object as an iterator.  In order to create as an iterator, you must implement the methods __iter__() and __next__().

To initialize the class/object in python, _init_() can be used.  

The above-mentioned _iter_() method acts similar to _init_() but always returns the iterator object itself.  

_next_() method also allows operations and must return the next item in the order.

Syntax

Class className:

def __iter__(self):

--  Operation -- 

return self

                                  def __next__(self):

-- Operation -- 

                 return x

Example 1

In this example, you will create an iterator that returns odd numbers starting from 1.

class randomNumbers:
  def __iter__(self):
    self.a = 1
    return self

  def __next__(self):
    x = self.a
    self.a += 2
    return x

myclass = randomNumbers ()
myiterator= iter(myclass)

print(‘Iterator in python’)
print(next(myiterator))
print((‘Iterator in python’)
print(next(myiterator))
print((‘Iterator in python’)

Here, the randomNumbers is an object/class which is being implemented with two methods _iter_() and _next_() for an iterator.

Now, execute this program to see the output.

Output

Example 2:

In this example, you will create an iterator that returns the iteration between the start and stop numbers.

class PizzaCounter: 

    def __init__(self, start, stop): 

        self.num = start 

        self.stop = stop 

    def __iter__(self): 

        return self

    def __next__(self):  

        if self.num > self.stop: 

            raise StopIteration 

        else: 

            self.num += 1

            return self.num - 1        

# Driver code 

if __name__ == '__main__' :    

    a, b = 2, 5

    pizzaCtr1 = PizzaCounter(a, b) 

    pizzaCtr2 = PizzaCounter(a, b) 

    # Method 1-to print the range without iter() 

    print ("Display the range without iter()") 

    for iter1 in pizzaCtr1: 

        print ("Eating Pizzas, couter ", iter1, end ="\n") 

    print ("\n Display the range using iter()\n") 

    # Method 2- using iter() 

    obj = iter(pizzaCtr2) 

    try: 

        while True:

            print ("Eating Pizzas, couter ", next(obj)) 

    except:  

        print ("\n Done Pizzas, GAME OVER")

Let us execute the above program and see the output.

Output

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StopIteration in Python

StopIteration is a statement that will be useful when you want to stop the iteration at state to prevent the iteration from going over and over.

If you don’t use a StopIteration statement, then the iteration will go forever in a for loop or if you have enough next() methods.

The StopIteration can be used in the next() method to prevent the iteration after a specific condition or termination statement.

Syntax is

class MyNumbers:
   def __iter__(self):

-- Operation -- 

     return self

   def __next__(self):
     Terminating Condition
      -- Operation –

    return x
     else:
       raise StopIteration

Let us see an example program and see the output.

In this example, you must create an iterator in Python to iterate up to 10 counters. When the iteration reaches 10, you should raise StopIteration to prevent further iteration.

Output

Conclusion

An iterator is a basic object that can be iterated over in Python. A data-returning object that returns data in one-at-a-time increments. An iterator is a set of countable values. Iterators are objects that can be iterated over, which means you can go through all of the values. A Python object that implements the iterator protocol, which includes the methods __iter__() and __next__, is known as an iterator ().

Iterators have the advantage of being energy efficient. You don’t have to memorize the entire number system to get all the odd numbers. You can have infinite objects in finite memory.

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