What is an iterator, and how to use Python iterator

An iterator in Python is an object that implements the iterator protocol, which consists of the methods __iter__() and __next__(). Iterators are used to iterate over a collection of items, such as elements in a list, keys in a dictionary, or lines in a file. In this tutorial, we'll show you how to create and use custom iterators in Python.

Create an iterator class: To create a custom iterator, define a class that implements the __iter__() and __next__() methods. The __iter__() method should return the iterator object itself (usually self), and the __next__() method should return the next value in the sequence. If there are no more items to return, the __next__() method should raise the StopIteration exception.

Example:

class CountUpTo:
    def __init__(self, limit):
        self.limit = limit
        self.current = 0

    def __iter__(self):
        return self

    def __next__(self):
        if self.current > self.limit:
            raise StopIteration
        else:
            self.current += 1
            return self.current - 1

Create an instance of the iterator class: Instantiate the iterator class with the desired parameters.

counter = CountUpTo(5)

Iterate over the iterator using a for loop: You can use a for loop to automatically iterate over the iterator. The loop will continue until the StopIteration exception is raised.

for number in counter:
    print(number)

Output:

Iterate over the iterator using the next() function: You can also use the next() function to manually iterate over the iterator, one item at a time.

counter = CountUpTo(3)
print(next(counter))  # Output: 0
print(next(counter))  # Output: 1
print(next(counter))  # Output: 2
print(next(counter))  # Output: 3

Handling StopIteration exception: When the iterator is exhausted, the next() function will raise a StopIteration exception. You can catch this exception to handle the end of the iteration gracefully.

counter = CountUpTo(1)
print(next(counter))  # Output: 0
print(next(counter))  # Output: 1
try:
    print(next(counter))
except StopIteration:
    print("Iteration is finished.")

Output:

0
1
Iteration is finished.

In this tutorial, you learned how to create and use custom iterators in Python by implementing the __iter__() and __next__() methods in a class. Iterators provide a memory-efficient and flexible way to work with sequences of items and can be used with built-in Python functions and control structures like for loops and comprehensions.

How to create an iterator in Python:

class MyIterator:
    def __init__(self, data):
        self.data = data
        self.index = 0

    def __iter__(self):
        return self

    def __next__(self):
        if self.index < len(self.data):
            result = self.data[self.index]
            self.index += 1
            return result
        else:
            raise StopIteration

my_list = [1, 2, 3, 4, 5]
my_iterator = MyIterator(my_list)

for item in my_iterator:
    print(item)

Iterating over objects in Python using iterators:

my_list = [1, 2, 3, 4, 5]
my_iterator = iter(my_list)

for item in my_iterator:
    print(item)

Iterating through lists with Python iterators:

my_list = [1, 2, 3, 4, 5]
my_iterator = iter(my_list)

for item in my_iterator:
    print(item)

Creating custom iterators in Python:

class MyIterator:
    def __init__(self, data):
        self.data = data
        self.index = 0

    def __iter__(self):
        return self

    def __next__(self):
        if self.index < len(self.data):
            result = self.data[self.index]
            self.index += 1
            return result
        else:
            raise StopIteration

my_list = [1, 2, 3, 4, 5]
my_iterator = MyIterator(my_list)

for item in my_iterator:
    print(item)

Working with for loops and iterators in Python:

my_list = [1, 2, 3, 4, 5]

for item in my_list:
    print(item)

Using the iter() function in Python:

my_list = [1, 2, 3, 4, 5]
my_iterator = iter(my_list)

for item in my_iterator:
    print(item)

Advanced iterator usage in Python:

class Fibonacci:
    def __init__(self):
        self.prev = 0
        self.current = 1

    def __iter__(self):
        return self

    def __next__(self):
        result = self.prev
        self.prev, self.current = self.current, self.prev + self.current
        return result

fib_sequence = Fibonacci()

for _ in range(10):
    print(next(fib_sequence))