#Python's Iterators and Iterable Objects

#Iterator

An iterator in Python is a tool used to traverse collection objects. It provides a unified way to access elements in a collection.

In Python, an object is considered an iterator if it implements the __next__ method. This method returns the next item in the sequence each time it is called, and raises a StopIteration exception when there are no more items.

You can retrieve the next item from an iterator using the built-in next function.

Example:

import io

# Iterator class
class Iterator:
    def __init__(self, stop):
        self.__stop = stop
        self.__current = 0
    
    # Return items one by one
    def __next__(self):
        if self.__current < self.__stop:
            self.__current += 1
            return self.__current - 1
        else:
            raise StopIteration

# Create an iterator object
iterator = Iterator(10)

# Iterate
while (value := next(iterator, None)) is not None:
    print(value)
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#Iterable Object

An iterable object is an object that contains an iterator. In Python, any object that implements the __iter__ method is considered iterable. This method is responsible for returning an iterator.

You can obtain an iterator from an iterable using the built-in iter function.

Example:

# Iterator class
class Iterator:
    def __init__(self, stop):
        self.__stop = stop
        self.__current = 0
    
    # Return items one by one
    def __next__(self):
        if self.__current < self.__stop:
            self.__current += 1
            return self.__current - 1
        else:
            raise StopIteration

# Iterable class
class Iterable:
    def __init__(self, stop):
        self.__iterator = Iterator(stop)

    def __iter__(self):
        return self.__iterator

# Create an iterable object
iterable = Iterable(10)

# for loop iteration
for value in iterable:
    print(value)
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It's not necessary to implement iterators and iterables as two separate classes. Often, the iterable object is its own iterator by having the __iter__ method return self.

For example:

# Object that is both iterable and an iterator
class Iterator:
    def __init__(self, stop):
        self.__stop = stop
        self.__current = 0
    
    def __next__(self):
        if self.__current < self.__stop:
            self.__current += 1
            return self.__current - 1
        else:
            raise StopIteration

    # Return self as iterator
    def __iter__(self):
        self.__current = 0  # Reset state
        return self

# Create an iterator
iterator = Iterator(10)

# for loop iteration
for value in iterator:
    print(value)
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