An Iterator in Python is an Object which contains a countable number of values or elements. You can use this Python iterator to Traverse all those elements.
The Python iterator uses the special methods called __iter__() and __next__() methods to iterate the object elements.
Python Iterables vs Iterator
Any object can be an iterable, if we can get an iterator from it. So far, we have seen the iterables called Lists, Tuples, Sets and Dictionaries. From these objects, you can call iterator or Iter.
In this article, we will show you, how to use Iterator in Python programming language. Here, we also show you, how to create our own iterators and infinity iterators with practical examples.
Python String Iterator Example
In python, strings are iterable objects. In this example, we are going to use the regular for loop to iterate each and every character in a string, and returns that character.
By default, or say, For loop implements the Iterator concept without your knowledge.
# Python Iterator Example string = 'tutorialgateway' for x in string: print(x, end = ' ')
OUTPUT
Python Iterators For loop Example 2
In this example, we used both for loop and iterators. In python, we have to use the next() function to return an element or value from an iterator.
Remember, next() function returns one item at a time. So, for n number of items you have to use n next() statements. Here, we used next() for one time so, it returns the first character from a string.
string = 'tutorialgateway'
for x in string:
print(x, end = ' ')
print("\n**** Iterator Example *****")
itr = iter(string)
print(next(itr))OUTPUT
Let me use next() to iterate all the characters in a string. This time, it will write the completed string.
string = 'tutorialgateway'
for x in string:
print(x, end = ' ')
print("\n**** Iterator Example *****")
itr = iter(string)
print(next(itr))
print(next(itr))
print(next(itr))
print(next(itr))
print(next(itr))
print(next(itr))
print(next(itr))
print(next(itr))
print(next(itr))
print(next(itr))
print(next(itr))
print(next(itr))
print(next(itr))
print(next(itr))
print(next(itr))OUTPUT
Python List Iterator
In this example, we will show you, how to iterate List items and prints 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))
OUTPUT
This example is same as above. However, this time, we used the __next__() special method. If you observe the last statement, we are trying to return next element that doesn’t exist. That’s why Python Iterator is calling 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__())
OUTPUT
Python Set Iterator
You can use Iterator to iterate the set items too. This program iterates the numbers in a Set and print 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__())OUTPUT
Tuple Iterator
Python also allows you to use this on Tuples as well. This program iterates Tuple items and prints each items 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))OUTPUT
Create Own Iterator in Python
This is a simple class called Counter. First, we declared a maximum value within the __init__ method.
The __iter__ method is used to initialise the value of an iterable object. For now, we set the number to 0. It means, Python Iterator will 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 will raise Otherwise, the number will be 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))
OUTPUT
Python Own Iterator Example 2
As you can see from the above screenshot, it is displaying numbers from 0 to 2. This is because, we used next(a) for three times only.
In this program, we used for loop to iterate the Counter class where maximum value is 10. This prints the values from 0 to 10. __iter__() starts at 0, and __next__() will print elements upto 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)
OUTPUT
Python Infinity Iterator
While you create your own iterator, you should always be careful with Infinity loops. If you forget to raise the StopIterator error then you will end up in infinity loops.
This is a simple example of infinity iterator. This example is same as above however, 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))
OUTPUT
Although, the above example is an infinite iterator, you might have not noticed it. This is because, we used the next() for three times only. So, let me use for loop to iterator that counter class.
class Counter: def __iter__(self): self.number = 0 return self def __next__(self): number = self.number self.number = number + 1 return number for t in Counter(): print(t)
OUTPUT
Now you can see the Python infinity iterator. This iterator will execute continuously.
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